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 $226.81   3.459%   $234.6554   $234.66   $234.65   $234.70  
  Purchase #2 $34.83   3.293%   $35.977   $35.98   $36.00   $36.00  
  Purchase #3 $222.27   9.316%   $242.9767   $242.98   $243.00   $243.00  
  Purchase #4 $82.97   3.590%   $85.9486   $85.95   $85.95   $85.90  
  Purchase #5 $22.63   7.242%   $24.2689   $24.27   $24.25   $24.30  
  Purchase #6 $20.93   11.417%   $23.3196   $23.32   $23.30   $23.30  
  Purchase #7 $167.69   9.780%   $184.0901   $184.09   $184.10   $184.10  
  7 purchase totals = $778.13       $831.2363   $831.25   $831.25   $831.30