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 $246.34   8.738%   $267.8652   $267.87   $267.85   $267.90  
  Purchase #2 $70.78   7.576%   $76.1423   $76.14   $76.15   $76.10  
  Purchase #3 $64.89   8.581%   $70.4582   $70.46   $70.45   $70.50  
  Purchase #4 $238.97   13.288%   $270.7243   $270.72   $270.70   $270.70  
  Purchase #5 $27.26   12.194%   $30.5841   $30.58   $30.60   $30.60  
  Purchase #6 $238.34   7.297%   $255.7317   $255.73   $255.75   $255.70  
  Purchase #7 $61.43   6.781%   $65.5956   $65.60   $65.60   $65.60  
  7 purchase totals = $948.01       $1,037.1014   $1,037.10   $1,037.10   $1,037.10