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 $209.77   11.607%   $234.118   $234.12   $234.10   $234.10  
  Purchase #2 $32.92   10.114%   $36.2495   $36.25   $36.25   $36.20  
  Purchase #3 $179.35   3.858%   $186.2693   $186.27   $186.25   $186.30  
  Purchase #4 $170.38   4.319%   $177.7387   $177.74   $177.75   $177.70  
  Purchase #5 $173.38   9.826%   $190.4163   $190.42   $190.40   $190.40  
  Purchase #6 $180.85   12.222%   $202.9535   $202.95   $202.95   $203.00  
  Purchase #7 $194.69   5.124%   $204.6659   $204.67   $204.65   $204.70  
  7 purchase totals = $1,141.34       $1,232.4112   $1,232.42   $1,232.35   $1,232.40