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 $120.83   13.230%   $136.8158   $136.82   $136.80   $136.80  
  Purchase #2 $90.97   4.653%   $95.2028   $95.20   $95.20   $95.20  
  Purchase #3 $116.36   3.142%   $120.016   $120.02   $120.00   $120.00  
  Purchase #4 $53.52   5.184%   $56.2945   $56.29   $56.30   $56.30  
  Purchase #5 $84.87   5.450%   $89.4954   $89.50   $89.50   $89.50  
  Purchase #6 $207.35   7.524%   $222.951   $222.95   $222.95   $223.00  
  Purchase #7 $193.44   6.723%   $206.445   $206.45   $206.45   $206.40  
  7 purchase totals = $867.34       $927.2205   $927.23   $927.20   $927.20