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 $210.89   12.502%   $237.2555   $237.26   $237.25   $237.30  
  Purchase #2 $125.82   12.236%   $141.2153   $141.22   $141.20   $141.20  
  Purchase #3 $206.87   4.217%   $215.5937   $215.59   $215.60   $215.60  
  Purchase #4 $206.28   4.836%   $216.2557   $216.26   $216.25   $216.30  
  Purchase #5 $168.74   8.413%   $182.9361   $182.94   $182.95   $182.90  
  Purchase #6 $43.54   3.396%   $45.0186   $45.02   $45.00   $45.00  
  Purchase #7 $187.52   3.446%   $193.9819   $193.98   $194.00   $194.00  
  7 purchase totals = $1,149.66       $1,232.2568   $1,232.27   $1,232.25   $1,232.30