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 $41.71   7.344%   $44.7732   $44.77   $44.75   $44.80  
  Purchase #2 $224.74   11.849%   $251.3694   $251.37   $251.35   $251.40  
  Purchase #3 $241.89   11.651%   $270.0726   $270.07   $270.05   $270.10  
  Purchase #4 $249.66   5.198%   $262.6373   $262.64   $262.65   $262.60  
  Purchase #5 $51.54   4.838%   $54.0335   $54.03   $54.05   $54.00  
  Purchase #6 $229.68   5.435%   $242.1631   $242.16   $242.15   $242.20  
  Purchase #7 $200.99   11.513%   $224.13   $224.13   $224.15   $224.10  
  7 purchase totals = $1,240.21       $1,349.1791   $1,349.17   $1,349.15   $1,349.20