Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $176.49   13.781%   $200.8121   $200.81   $200.80   $200.80  
  Purchase #2 $176.52   9.317%   $192.9664   $192.97   $192.95   $193.00  
  Purchase #3 $116.86   12.782%   $131.797   $131.80   $131.80   $131.80  
  Purchase #4 $218.34   13.398%   $247.5932   $247.59   $247.60   $247.60  
  Purchase #5 $169.84   9.159%   $185.3956   $185.40   $185.40   $185.40  
  Purchase #6 $221.86   13.368%   $251.5182   $251.52   $251.50   $251.50  
  Purchase #7 $139.49   10.328%   $153.8965   $153.90   $153.90   $153.90  
  7 purchase totals = $1,219.40       $1,363.9790   $1,363.99   $1,363.95   $1,364.00