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 $76.40   12.437%   $85.9019   $85.90   $85.90   $85.90  
  Purchase #2 $241.49   6.111%   $256.2475   $256.25   $256.25   $256.20  
  Purchase #3 $61.59   3.810%   $63.9366   $63.94   $63.95   $63.90  
  Purchase #4 $237.59   8.209%   $257.0938   $257.09   $257.10   $257.10  
  Purchase #5 $132.73   10.115%   $146.1556   $146.16   $146.15   $146.20  
  Purchase #6 $216.58   11.317%   $241.0904   $241.09   $241.10   $241.10  
  Purchase #7 $10.54   12.402%   $11.8472   $11.85   $11.85   $11.80  
  7 purchase totals = $976.92       $1,062.2730   $1,062.28   $1,062.30   $1,062.20