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 $39.27   13.213%   $44.4587   $44.46   $44.45   $44.50  
  Purchase #2 $126.42   4.679%   $132.3352   $132.34   $132.35   $132.30  
  Purchase #3 $170.63   9.327%   $186.5447   $186.54   $186.55   $186.50  
  Purchase #4 $225.90   12.467%   $254.063   $254.06   $254.05   $254.10  
  Purchase #5 $59.52   12.283%   $66.8308   $66.83   $66.85   $66.80  
  Purchase #6 $172.49   3.626%   $178.7445   $178.74   $178.75   $178.70  
  Purchase #7 $153.62   4.682%   $160.8125   $160.81   $160.80   $160.80  
  7 purchase totals = $947.85       $1,023.7894   $1,023.78   $1,023.80   $1,023.70