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 $185.84   12.751%   $209.5365   $209.54   $209.55   $209.50  
  Purchase #2 $195.61   4.735%   $204.8721   $204.87   $204.85   $204.90  
  Purchase #3 $51.77   12.530%   $58.2568   $58.26   $58.25   $58.30  
  Purchase #4 $58.94   3.827%   $61.1956   $61.20   $61.20   $61.20  
  Purchase #5 $111.90   7.319%   $120.09   $120.09   $120.10   $120.10  
  Purchase #6 $46.40   11.283%   $51.6353   $51.64   $51.65   $51.60  
  Purchase #7 $201.63   9.315%   $220.4118   $220.41   $220.40   $220.40  
  7 purchase totals = $852.09       $925.9981   $926.01   $926.00   $926.00