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 $173.82   12.621%   $195.7578   $195.76   $195.75   $195.80  
  Purchase #2 $203.38   10.297%   $224.322   $224.32   $224.30   $224.30  
  Purchase #3 $177.84   6.201%   $188.8679   $188.87   $188.85   $188.90  
  Purchase #4 $213.74   13.773%   $243.1784   $243.18   $243.20   $243.20  
  Purchase #5 $221.65   3.263%   $228.8824   $228.88   $228.90   $228.90  
  Purchase #6 $135.32   11.227%   $150.5124   $150.51   $150.50   $150.50  
  Purchase #7 $84.91   11.421%   $94.6076   $94.61   $94.60   $94.60  
  7 purchase totals = $1,210.66       $1,326.1285   $1,326.13   $1,326.10   $1,326.20