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 $67.78   12.613%   $76.3291   $76.33   $76.35   $76.30  
  Purchase #2 $241.88   5.536%   $255.2705   $255.27   $255.25   $255.30  
  Purchase #3 $152.73   11.622%   $170.4803   $170.48   $170.50   $170.50  
  Purchase #4 $136.82   5.728%   $144.657   $144.66   $144.65   $144.70  
  Purchase #5 $235.56   12.265%   $264.4514   $264.45   $264.45   $264.50  
  Purchase #6 $205.68   3.662%   $213.212   $213.21   $213.20   $213.20  
  Purchase #7 $54.33   7.121%   $58.1988   $58.20   $58.20   $58.20  
  7 purchase totals = $1,094.78       $1,182.5991   $1,182.60   $1,182.60   $1,182.70