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 $55.39   5.306%   $58.329   $58.33   $58.35   $58.30  
  Purchase #2 $235.63   11.471%   $262.6591   $262.66   $262.65   $262.70  
  Purchase #3 $127.49   3.318%   $131.7201   $131.72   $131.70   $131.70  
  Purchase #4 $127.47   11.561%   $142.2068   $142.21   $142.20   $142.20  
  Purchase #5 $23.66   10.837%   $26.224   $26.22   $26.20   $26.20  
  Purchase #6 $91.38   11.104%   $101.5268   $101.53   $101.55   $101.50  
  Purchase #7 $141.65   6.408%   $150.7269   $150.73   $150.75   $150.70  
  7 purchase totals = $802.67       $873.3927   $873.40   $873.40   $873.30