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 $45.77   13.641%   $52.0135   $52.01   $52.00   $52.00  
  Purchase #2 $212.88   3.141%   $219.5666   $219.57   $219.55   $219.60  
  Purchase #3 $8.99   9.368%   $9.8322   $9.83   $9.85   $9.80  
  Purchase #4 $119.84   11.822%   $134.0075   $134.01   $134.00   $134.00  
  Purchase #5 $47.74   5.694%   $50.4583   $50.46   $50.45   $50.50  
  Purchase #6 $240.86   10.824%   $266.9307   $266.93   $266.95   $266.90  
  Purchase #7 $33.72   5.562%   $35.5955   $35.60   $35.60   $35.60  
  7 purchase totals = $709.80       $768.4043   $768.41   $768.40   $768.40