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 $88.60   6.819%   $94.6416   $94.64   $94.65   $94.60  
  Purchase #2 $107.46   10.508%   $118.7519   $118.75   $118.75   $118.80  
  Purchase #3 $107.26   7.836%   $115.6649   $115.66   $115.65   $115.70  
  Purchase #4 $199.33   5.650%   $210.5921   $210.59   $210.60   $210.60  
  Purchase #5 $205.71   8.597%   $223.3949   $223.39   $223.40   $223.40  
  Purchase #6 $65.50   12.146%   $73.4556   $73.46   $73.45   $73.50  
  Purchase #7 $175.57   10.869%   $194.6527   $194.65   $194.65   $194.70  
  7 purchase totals = $949.43       $1,031.1537   $1,031.14   $1,031.15   $1,031.30