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 $61.43   8.575%   $66.6976   $66.70   $66.70   $66.70  
  Purchase #2 $209.89   12.289%   $235.6834   $235.68   $235.70   $235.70  
  Purchase #3 $23.30   8.346%   $25.2446   $25.24   $25.25   $25.20  
  Purchase #4 $106.49   7.799%   $114.7952   $114.80   $114.80   $114.80  
  Purchase #5 $226.79   11.738%   $253.4106   $253.41   $253.40   $253.40  
  Purchase #6 $6.56   11.597%   $7.3208   $7.32   $7.30   $7.30  
  Purchase #7 $54.91   9.749%   $60.2632   $60.26   $60.25   $60.30  
  7 purchase totals = $689.37       $763.4154   $763.41   $763.40   $763.40