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 $162.48   12.144%   $182.2116   $182.21   $182.20   $182.20  
  Purchase #2 $61.91   13.541%   $70.2932   $70.29   $70.30   $70.30  
  Purchase #3 $182.67   6.658%   $194.8322   $194.83   $194.85   $194.80  
  Purchase #4 $93.46   4.691%   $97.8442   $97.84   $97.85   $97.80  
  Purchase #5 $57.81   5.656%   $61.0797   $61.08   $61.10   $61.10  
  Purchase #6 $151.89   12.143%   $170.334   $170.33   $170.35   $170.30  
  Purchase #7 $60.51   13.497%   $68.677   $68.68   $68.70   $68.70  
  7 purchase totals = $770.73       $845.2719   $845.26   $845.35   $845.20