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 $211.42   3.536%   $218.8958   $218.90   $218.90   $218.90  
  Purchase #2 $18.49   6.722%   $19.7329   $19.73   $19.75   $19.70  
  Purchase #3 $95.60   11.841%   $106.92   $106.92   $106.90   $106.90  
  Purchase #4 $90.79   6.587%   $96.7703   $96.77   $96.75   $96.80  
  Purchase #5 $45.99   4.218%   $47.9299   $47.93   $47.95   $47.90  
  Purchase #6 $188.28   4.430%   $196.6208   $196.62   $196.60   $196.60  
  Purchase #7 $43.43   12.725%   $48.9565   $48.96   $48.95   $49.00  
  7 purchase totals = $694.00       $735.8262   $735.83   $735.80   $735.80