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 $7.38   5.417%   $7.7798   $7.78   $7.80   $7.80  
  Purchase #2 $27.69   12.578%   $31.1728   $31.17   $31.15   $31.20  
  Purchase #3 $217.42   4.582%   $227.3822   $227.38   $227.40   $227.40  
  Purchase #4 $109.43   5.487%   $115.4344   $115.43   $115.45   $115.40  
  Purchase #5 $13.30   9.619%   $14.5793   $14.58   $14.60   $14.60  
  Purchase #6 $205.78   4.761%   $215.5772   $215.58   $215.60   $215.60  
  Purchase #7 $77.62   10.492%   $85.7639   $85.76   $85.75   $85.80  
  7 purchase totals = $658.62       $697.6896   $697.68   $697.75   $697.80