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 $26.76   12.470%   $30.097   $30.10   $30.10   $30.10  
  Purchase #2 $210.26   10.664%   $232.6821   $232.68   $232.70   $232.70  
  Purchase #3 $64.93   3.781%   $67.385   $67.39   $67.40   $67.40  
  Purchase #4 $101.35   8.370%   $109.833   $109.83   $109.85   $109.80  
  Purchase #5 $168.70   6.713%   $180.0248   $180.02   $180.00   $180.00  
  Purchase #6 $241.66   9.371%   $264.306   $264.31   $264.30   $264.30  
  Purchase #7 $65.41   10.142%   $72.0439   $72.04   $72.05   $72.00  
  7 purchase totals = $879.07       $956.3718   $956.37   $956.40   $956.30