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 $174.88   4.749%   $183.1851   $183.19   $183.20   $183.20  
  Purchase #2 $234.25   8.837%   $254.9507   $254.95   $254.95   $255.00  
  Purchase #3 $208.93   6.372%   $222.243   $222.24   $222.25   $222.20  
  Purchase #4 $22.68   10.282%   $25.012   $25.01   $25.00   $25.00  
  Purchase #5 $92.26   7.535%   $99.2118   $99.21   $99.20   $99.20  
  Purchase #6 $100.42   9.249%   $109.7078   $109.71   $109.70   $109.70  
  Purchase #7 $133.83   9.713%   $146.8289   $146.83   $146.85   $146.80  
  7 purchase totals = $967.25       $1,041.1393   $1,041.14   $1,041.15   $1,041.10