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 $236.25   6.795%   $252.3032   $252.30   $252.30   $252.30  
  Purchase #2 $249.26   7.335%   $267.5432   $267.54   $267.55   $267.50  
  Purchase #3 $64.98   4.586%   $67.96   $67.96   $67.95   $68.00  
  Purchase #4 $232.48   10.424%   $256.7137   $256.71   $256.70   $256.70  
  Purchase #5 $88.26   6.233%   $93.7612   $93.76   $93.75   $93.80  
  Purchase #6 $141.77   4.670%   $148.3907   $148.39   $148.40   $148.40  
  Purchase #7 $173.45   6.334%   $184.4363   $184.44   $184.45   $184.40  
  7 purchase totals = $1,186.45       $1,271.1083   $1,271.10   $1,271.10   $1,271.10