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 $192.69   4.548%   $201.4535   $201.45   $201.45   $201.50  
  Purchase #2 $173.92   11.465%   $193.8599   $193.86   $193.85   $193.90  
  Purchase #3 $59.78   13.688%   $67.9627   $67.96   $67.95   $68.00  
  Purchase #4 $44.36   10.382%   $48.9655   $48.97   $48.95   $49.00  
  Purchase #5 $211.61   4.853%   $221.8794   $221.88   $221.90   $221.90  
  Purchase #6 $19.31   6.503%   $20.5657   $20.57   $20.55   $20.60  
  Purchase #7 $216.59   4.222%   $225.7344   $225.73   $225.75   $225.70  
  7 purchase totals = $918.26       $980.4211   $980.42   $980.40   $980.60