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 $209.34   10.315%   $230.9334   $230.93   $230.95   $230.90  
  Purchase #2 $171.78   9.768%   $188.5595   $188.56   $188.55   $188.60  
  Purchase #3 $247.83   9.183%   $270.5882   $270.59   $270.60   $270.60  
  Purchase #4 $210.59   11.136%   $234.0413   $234.04   $234.05   $234.00  
  Purchase #5 $69.47   6.685%   $74.1141   $74.11   $74.10   $74.10  
  Purchase #6 $98.62   6.760%   $105.2867   $105.29   $105.30   $105.30  
  Purchase #7 $130.85   9.760%   $143.621   $143.62   $143.60   $143.60  
  7 purchase totals = $1,138.48       $1,247.1442   $1,247.14   $1,247.15   $1,247.10