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 $59.97   6.381%   $63.7967   $63.80   $63.80   $63.80  
  Purchase #2 $144.47   4.276%   $150.6475   $150.65   $150.65   $150.60  
  Purchase #3 $232.93   8.176%   $251.9744   $251.97   $251.95   $252.00  
  Purchase #4 $246.39   3.115%   $254.065   $254.07   $254.05   $254.10  
  Purchase #5 $29.88   13.329%   $33.8627   $33.86   $33.85   $33.90  
  Purchase #6 $44.53   6.774%   $47.5465   $47.55   $47.55   $47.50  
  Purchase #7 $130.40   8.299%   $141.2219   $141.22   $141.20   $141.20  
  7 purchase totals = $888.57       $943.1147   $943.12   $943.05   $943.10