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 $44.78   6.256%   $47.5814   $47.58   $47.60   $47.60  
  Purchase #2 $118.48   6.758%   $126.4869   $126.49   $126.50   $126.50  
  Purchase #3 $103.66   3.766%   $107.5638   $107.56   $107.55   $107.60  
  Purchase #4 $84.88   4.367%   $88.5867   $88.59   $88.60   $88.60  
  Purchase #5 $6.26   13.351%   $7.0958   $7.10   $7.10   $7.10  
  Purchase #6 $184.77   8.170%   $199.8657   $199.87   $199.85   $199.90  
  Purchase #7 $159.58   10.136%   $175.755   $175.76   $175.75   $175.80  
  7 purchase totals = $702.41       $752.9353   $752.95   $752.95   $753.10