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 $206.94   12.325%   $232.4454   $232.45   $232.45   $232.40  
  Purchase #2 $213.94   5.608%   $225.9378   $225.94   $225.95   $225.90  
  Purchase #3 $216.39   3.637%   $224.2601   $224.26   $224.25   $224.30  
  Purchase #4 $150.79   9.603%   $165.2704   $165.27   $165.25   $165.30  
  Purchase #5 $104.46   5.503%   $110.2084   $110.21   $110.20   $110.20  
  Purchase #6 $161.58   12.811%   $182.28   $182.28   $182.30   $182.30  
  Purchase #7 $151.83   12.624%   $170.997   $171.00   $171.00   $171.00  
  7 purchase totals = $1,205.93       $1,311.3991   $1,311.41   $1,311.40   $1,311.40