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 $61.26   11.583%   $68.3557   $68.36   $68.35   $68.40  
  Purchase #2 $48.52   4.511%   $50.7087   $50.71   $50.70   $50.70  
  Purchase #3 $58.96   13.607%   $66.9827   $66.98   $67.00   $67.00  
  Purchase #4 $206.87   4.548%   $216.2784   $216.28   $216.30   $216.30  
  Purchase #5 $50.79   12.826%   $57.3043   $57.30   $57.30   $57.30  
  Purchase #6 $6.49   10.836%   $7.1933   $7.19   $7.20   $7.20  
  Purchase #7 $115.79   3.326%   $119.6412   $119.64   $119.65   $119.60  
  7 purchase totals = $548.68       $586.4643   $586.46   $586.50   $586.50