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 $135.45   13.319%   $153.4906   $153.49   $153.50   $153.50  
  Purchase #2 $101.99   7.420%   $109.5577   $109.56   $109.55   $109.60  
  Purchase #3 $95.80   11.656%   $106.9664   $106.97   $106.95   $107.00  
  Purchase #4 $152.87   6.313%   $162.5207   $162.52   $162.50   $162.50  
  Purchase #5 $54.70   13.525%   $62.0982   $62.10   $62.10   $62.10  
  Purchase #6 $9.59   5.622%   $10.1291   $10.13   $10.15   $10.10  
  Purchase #7 $214.45   11.227%   $238.5263   $238.53   $238.55   $238.50  
  7 purchase totals = $764.85       $843.2890   $843.30   $843.30   $843.30