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 $202.98   11.128%   $225.5676   $225.57   $225.55   $225.60  
  Purchase #2 $250.43   10.555%   $276.8629   $276.86   $276.85   $276.90  
  Purchase #3 $24.73   6.796%   $26.4107   $26.41   $26.40   $26.40  
  Purchase #4 $93.41   12.823%   $105.388   $105.39   $105.40   $105.40  
  Purchase #5 $133.88   10.753%   $148.2761   $148.28   $148.30   $148.30  
  Purchase #6 $89.59   5.862%   $94.8418   $94.84   $94.85   $94.80  
  Purchase #7 $171.30   13.729%   $194.8178   $194.82   $194.80   $194.80  
  7 purchase totals = $966.32       $1,072.1649   $1,072.17   $1,072.15   $1,072.20