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 $61.49   11.742%   $68.7102   $68.71   $68.70   $68.70  
  Purchase #2 $79.64   5.490%   $84.0122   $84.01   $84.00   $84.00  
  Purchase #3 $7.93   7.559%   $8.5294   $8.53   $8.55   $8.50  
  Purchase #4 $141.25   10.246%   $155.7225   $155.72   $155.70   $155.70  
  Purchase #5 $233.48   11.756%   $260.9279   $260.93   $260.95   $260.90  
  Purchase #6 $112.33   3.521%   $116.2851   $116.29   $116.30   $116.30  
  Purchase #7 $244.37   5.590%   $258.0303   $258.03   $258.05   $258.00  
  7 purchase totals = $880.49       $952.2176   $952.22   $952.25   $952.10