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 $187.42   12.377%   $210.617   $210.62   $210.60   $210.60  
  Purchase #2 $107.45   8.729%   $116.8293   $116.83   $116.85   $116.80  
  Purchase #3 $78.37   11.676%   $87.5205   $87.52   $87.50   $87.50  
  Purchase #4 $196.92   11.189%   $218.9534   $218.95   $218.95   $219.00  
  Purchase #5 $45.83   11.377%   $51.0441   $51.04   $51.05   $51.00  
  Purchase #6 $91.68   12.759%   $103.3775   $103.38   $103.40   $103.40  
  Purchase #7 $82.68   6.389%   $87.9624   $87.96   $87.95   $88.00  
  7 purchase totals = $790.35       $876.3042   $876.30   $876.30   $876.30