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 $246.89   6.807%   $263.6958   $263.70   $263.70   $263.70  
  Purchase #2 $126.42   7.462%   $135.8535   $135.85   $135.85   $135.90  
  Purchase #3 $127.70   11.815%   $142.7878   $142.79   $142.80   $142.80  
  Purchase #4 $130.82   7.602%   $140.7649   $140.76   $140.75   $140.80  
  Purchase #5 $43.30   9.804%   $47.5451   $47.55   $47.55   $47.50  
  Purchase #6 $236.80   8.414%   $256.7244   $256.72   $256.70   $256.70  
  Purchase #7 $82.30   7.125%   $88.1639   $88.16   $88.15   $88.20  
  7 purchase totals = $994.23       $1,075.5354   $1,075.53   $1,075.50   $1,075.60