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 $61.74   5.459%   $65.1104   $65.11   $65.10   $65.10  
  Purchase #2 $14.95   8.559%   $16.2296   $16.23   $16.25   $16.20  
  Purchase #3 $240.88   8.260%   $260.7767   $260.78   $260.80   $260.80  
  Purchase #4 $68.73   6.392%   $73.1232   $73.12   $73.10   $73.10  
  Purchase #5 $229.92   6.128%   $244.0095   $244.01   $244.00   $244.00  
  Purchase #6 $134.65   3.442%   $139.2847   $139.28   $139.30   $139.30  
  Purchase #7 $64.68   10.484%   $71.4611   $71.46   $71.45   $71.50  
  7 purchase totals = $815.55       $869.9952   $869.99   $870.00   $870.00