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 $110.86   11.513%   $123.6233   $123.62   $123.60   $123.60  
  Purchase #2 $220.39   5.291%   $232.0508   $232.05   $232.05   $232.10  
  Purchase #3 $116.35   12.626%   $131.0404   $131.04   $131.05   $131.00  
  Purchase #4 $221.40   5.865%   $234.3851   $234.39   $234.40   $234.40  
  Purchase #5 $247.29   4.732%   $258.9918   $258.99   $259.00   $259.00  
  Purchase #6 $153.35   8.730%   $166.7375   $166.74   $166.75   $166.70  
  Purchase #7 $150.34   5.105%   $158.0149   $158.01   $158.00   $158.00  
  7 purchase totals = $1,219.98       $1,304.8438   $1,304.84   $1,304.85   $1,304.80