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 $61.44   13.404%   $69.6754   $69.68   $69.70   $69.70  
  Purchase #2 $137.94   13.325%   $156.3205   $156.32   $156.30   $156.30  
  Purchase #3 $236.71   8.122%   $255.9356   $255.94   $255.95   $255.90  
  Purchase #4 $36.42   3.186%   $37.5803   $37.58   $37.60   $37.60  
  Purchase #5 $20.70   8.487%   $22.4568   $22.46   $22.45   $22.50  
  Purchase #6 $43.78   9.339%   $47.8686   $47.87   $47.85   $47.90  
  Purchase #7 $201.39   12.165%   $225.8891   $225.89   $225.90   $225.90  
  7 purchase totals = $738.38       $815.7263   $815.74   $815.75   $815.80