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 $236.57   9.379%   $258.7579   $258.76   $258.75   $258.80  
  Purchase #2 $171.72   7.609%   $184.7862   $184.79   $184.80   $184.80  
  Purchase #3 $160.95   4.186%   $167.6874   $167.69   $167.70   $167.70  
  Purchase #4 $239.68   7.684%   $258.097   $258.10   $258.10   $258.10  
  Purchase #5 $197.80   4.347%   $206.3984   $206.40   $206.40   $206.40  
  Purchase #6 $245.43   4.486%   $256.44   $256.44   $256.45   $256.40  
  Purchase #7 $150.27   8.333%   $162.792   $162.79   $162.80   $162.80  
  7 purchase totals = $1,402.42       $1,494.9589   $1,494.97   $1,495.00   $1,495.00