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 $206.97   12.230%   $232.2824   $232.28   $232.30   $232.30  
  Purchase #2 $107.42   13.531%   $121.955   $121.96   $121.95   $122.00  
  Purchase #3 $60.40   6.392%   $64.2608   $64.26   $64.25   $64.30  
  Purchase #4 $187.51   6.243%   $199.2162   $199.22   $199.20   $199.20  
  Purchase #5 $65.87   4.590%   $68.8934   $68.89   $68.90   $68.90  
  Purchase #6 $244.60   6.409%   $260.2764   $260.28   $260.30   $260.30  
  Purchase #7 $225.38   11.428%   $251.1364   $251.14   $251.15   $251.10  
  7 purchase totals = $1,098.15       $1,198.0206   $1,198.03   $1,198.05   $1,198.10