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 $208.79   13.372%   $236.7094   $236.71   $236.70   $236.70  
  Purchase #2 $10.62   3.362%   $10.977   $10.98   $11.00   $11.00  
  Purchase #3 $84.60   5.699%   $89.4214   $89.42   $89.40   $89.40  
  Purchase #4 $211.75   7.362%   $227.339   $227.34   $227.35   $227.30  
  Purchase #5 $190.34   13.872%   $216.744   $216.74   $216.75   $216.70  
  Purchase #6 $40.35   11.820%   $45.1194   $45.12   $45.10   $45.10  
  Purchase #7 $11.61   8.211%   $12.5633   $12.56   $12.55   $12.60  
  7 purchase totals = $758.06       $838.8735   $838.87   $838.85   $838.80