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 $66.82   11.525%   $74.521   $74.52   $74.50   $74.50  
  Purchase #2 $39.96   6.839%   $42.6929   $42.69   $42.70   $42.70  
  Purchase #3 $250.27   9.176%   $273.2348   $273.23   $273.25   $273.20  
  Purchase #4 $58.41   4.497%   $61.0367   $61.04   $61.05   $61.00  
  Purchase #5 $201.49   13.477%   $228.6448   $228.64   $228.65   $228.60  
  Purchase #6 $117.94   7.523%   $126.8126   $126.81   $126.80   $126.80  
  Purchase #7 $191.81   9.415%   $209.8689   $209.87   $209.85   $209.90  
  7 purchase totals = $926.70       $1,016.8117   $1,016.80   $1,016.80   $1,016.70