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 $43.71   9.717%   $47.9573   $47.96   $47.95   $48.00  
  Purchase #2 $66.86   3.866%   $69.4448   $69.44   $69.45   $69.40  
  Purchase #3 $222.29   6.734%   $237.259   $237.26   $237.25   $237.30  
  Purchase #4 $178.40   7.293%   $191.4107   $191.41   $191.40   $191.40  
  Purchase #5 $108.68   5.512%   $114.6704   $114.67   $114.65   $114.70  
  Purchase #6 $84.49   3.311%   $87.2875   $87.29   $87.30   $87.30  
  Purchase #7 $26.71   7.374%   $28.6796   $28.68   $28.70   $28.70  
  7 purchase totals = $731.14       $776.7093   $776.71   $776.70   $776.80