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 $187.93   11.188%   $208.9556   $208.96   $208.95   $209.00  
  Purchase #2 $211.67   6.368%   $225.1491   $225.15   $225.15   $225.10  
  Purchase #3 $224.43   11.368%   $249.9432   $249.94   $249.95   $249.90  
  Purchase #4 $69.64   9.148%   $76.0107   $76.01   $76.00   $76.00  
  Purchase #5 $24.73   10.678%   $27.3707   $27.37   $27.35   $27.40  
  Purchase #6 $250.60   11.647%   $279.7874   $279.79   $279.80   $279.80  
  Purchase #7 $50.56   4.292%   $52.73   $52.73   $52.75   $52.70  
  7 purchase totals = $1,019.56       $1,119.9467   $1,119.95   $1,119.95   $1,119.90