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 $28.85   13.443%   $32.7283   $32.73   $32.75   $32.70  
  Purchase #2 $120.99   12.297%   $135.8681   $135.87   $135.85   $135.90  
  Purchase #3 $94.87   3.174%   $97.8812   $97.88   $97.90   $97.90  
  Purchase #4 $197.88   8.230%   $214.1655   $214.17   $214.15   $214.20  
  Purchase #5 $229.96   11.506%   $256.4192   $256.42   $256.40   $256.40  
  Purchase #6 $59.67   12.447%   $67.0971   $67.10   $67.10   $67.10  
  Purchase #7 $241.80   5.305%   $254.6275   $254.63   $254.65   $254.60  
  7 purchase totals = $974.02       $1,058.7869   $1,058.80   $1,058.80   $1,058.80