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 $60.52   12.832%   $68.2859   $68.29   $68.30   $68.30  
  Purchase #2 $191.51   10.119%   $210.8889   $210.89   $210.90   $210.90  
  Purchase #3 $224.42   4.420%   $234.3394   $234.34   $234.35   $234.30  
  Purchase #4 $160.99   11.825%   $180.0271   $180.03   $180.05   $180.00  
  Purchase #5 $211.35   7.163%   $226.489   $226.49   $226.50   $226.50  
  Purchase #6 $46.84   7.340%   $50.2781   $50.28   $50.30   $50.30  
  Purchase #7 $239.26   8.871%   $260.4848   $260.48   $260.50   $260.50  
  7 purchase totals = $1,134.89       $1,230.7932   $1,230.80   $1,230.90   $1,230.80