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 $59.29   3.305%   $61.2495   $61.25   $61.25   $61.20  
  Purchase #2 $148.59   4.840%   $155.7818   $155.78   $155.80   $155.80  
  Purchase #3 $23.74   12.672%   $26.7483   $26.75   $26.75   $26.70  
  Purchase #4 $174.77   11.199%   $194.3425   $194.34   $194.35   $194.30  
  Purchase #5 $104.98   8.508%   $113.9117   $113.91   $113.90   $113.90  
  Purchase #6 $74.50   3.456%   $77.0747   $77.07   $77.05   $77.10  
  Purchase #7 $115.37   12.528%   $129.8236   $129.82   $129.80   $129.80  
  7 purchase totals = $701.24       $758.9321   $758.92   $758.90   $758.80