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 $231.89   10.806%   $256.948   $256.95   $256.95   $256.90  
  Purchase #2 $62.25   10.313%   $68.6698   $68.67   $68.65   $68.70  
  Purchase #3 $135.63   12.175%   $152.143   $152.14   $152.15   $152.10  
  Purchase #4 $153.64   12.708%   $173.1646   $173.16   $173.15   $173.20  
  Purchase #5 $141.58   9.480%   $155.0018   $155.00   $155.00   $155.00  
  Purchase #6 $71.41   10.851%   $79.1587   $79.16   $79.15   $79.20  
  Purchase #7 $165.97   7.546%   $178.4941   $178.49   $178.50   $178.50  
  7 purchase totals = $962.37       $1,063.5800   $1,063.57   $1,063.55   $1,063.60