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 $95.35   7.237%   $102.2505   $102.25   $102.25   $102.30  
  Purchase #2 $191.82   4.105%   $199.6942   $199.69   $199.70   $199.70  
  Purchase #3 $58.29   9.483%   $63.8176   $63.82   $63.80   $63.80  
  Purchase #4 $222.66   4.450%   $232.5684   $232.57   $232.55   $232.60  
  Purchase #5 $65.40   8.610%   $71.0309   $71.03   $71.05   $71.00  
  Purchase #6 $196.76   13.829%   $223.9699   $223.97   $223.95   $224.00  
  Purchase #7 $116.85   10.404%   $129.0071   $129.01   $129.00   $129.00  
  7 purchase totals = $947.13       $1,022.3386   $1,022.34   $1,022.30   $1,022.40