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 $244.91   7.771%   $263.942   $263.94   $263.95   $263.90  
  Purchase #2 $57.30   6.347%   $60.9368   $60.94   $60.95   $60.90  
  Purchase #3 $181.92   5.513%   $191.9492   $191.95   $191.95   $191.90  
  Purchase #4 $249.65   3.161%   $257.5414   $257.54   $257.55   $257.50  
  Purchase #5 $41.66   7.818%   $44.917   $44.92   $44.90   $44.90  
  Purchase #6 $20.79   4.131%   $21.6488   $21.65   $21.65   $21.60  
  Purchase #7 $222.51   4.495%   $232.5118   $232.51   $232.50   $232.50  
  7 purchase totals = $1,018.74       $1,073.4470   $1,073.45   $1,073.45   $1,073.20