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 $57.26   8.321%   $62.0246   $62.02   $62.00   $62.00  
  Purchase #2 $32.44   11.195%   $36.0717   $36.07   $36.05   $36.10  
  Purchase #3 $206.71   7.733%   $222.6949   $222.69   $222.70   $222.70  
  Purchase #4 $94.52   9.492%   $103.4918   $103.49   $103.50   $103.50  
  Purchase #5 $244.38   11.832%   $273.295   $273.30   $273.30   $273.30  
  Purchase #6 $80.77   13.703%   $91.8379   $91.84   $91.85   $91.80  
  Purchase #7 $53.69   3.667%   $55.6588   $55.66   $55.65   $55.70  
  7 purchase totals = $769.77       $845.0747   $845.07   $845.05   $845.10