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 $217.58   12.591%   $244.9755   $244.98   $245.00   $245.00  
  Purchase #2 $23.50   7.550%   $25.2743   $25.27   $25.25   $25.30  
  Purchase #3 $98.66   13.190%   $111.6733   $111.67   $111.65   $111.70  
  Purchase #4 $61.78   13.694%   $70.2402   $70.24   $70.25   $70.20  
  Purchase #5 $202.99   4.496%   $212.1164   $212.12   $212.10   $212.10  
  Purchase #6 $52.29   12.844%   $59.0061   $59.01   $59.00   $59.00  
  Purchase #7 $25.37   9.444%   $27.7659   $27.77   $27.75   $27.80  
  7 purchase totals = $682.17       $751.0517   $751.06   $751.00   $751.10