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 $250.34   8.155%   $270.7552   $270.76   $270.75   $270.80  
  Purchase #2 $213.91   8.504%   $232.1009   $232.10   $232.10   $232.10  
  Purchase #3 $39.33   4.820%   $41.2257   $41.23   $41.25   $41.20  
  Purchase #4 $101.71   9.756%   $111.6328   $111.63   $111.65   $111.60  
  Purchase #5 $214.65   9.461%   $234.958   $234.96   $234.95   $235.00  
  Purchase #6 $164.48   13.370%   $186.471   $186.47   $186.45   $186.50  
  Purchase #7 $165.70   12.450%   $186.3297   $186.33   $186.35   $186.30  
  7 purchase totals = $1,150.12       $1,263.4733   $1,263.48   $1,263.50   $1,263.50