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 $248.75   10.779%   $275.5628   $275.56   $275.55   $275.60  
  Purchase #2 $223.63   3.828%   $232.1906   $232.19   $232.20   $232.20  
  Purchase #3 $165.82   3.616%   $171.8161   $171.82   $171.80   $171.80  
  Purchase #4 $179.44   11.739%   $200.5045   $200.50   $200.50   $200.50  
  Purchase #5 $96.71   11.330%   $107.6672   $107.67   $107.65   $107.70  
  Purchase #6 $84.51   5.832%   $89.4386   $89.44   $89.45   $89.40  
  Purchase #7 $248.40   12.767%   $280.1132   $280.11   $280.10   $280.10  
  7 purchase totals = $1,247.26       $1,357.2930   $1,357.29   $1,357.25   $1,357.30