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 $250.69   4.613%   $262.2543   $262.25   $262.25   $262.30  
  Purchase #2 $82.53   10.784%   $91.43   $91.43   $91.45   $91.40  
  Purchase #3 $70.70   3.623%   $73.2615   $73.26   $73.25   $73.30  
  Purchase #4 $145.62   6.453%   $155.0169   $155.02   $155.00   $155.00  
  Purchase #5 $8.52   9.569%   $9.3353   $9.34   $9.35   $9.30  
  Purchase #6 $122.37   8.352%   $132.5903   $132.59   $132.60   $132.60  
  Purchase #7 $166.94   13.704%   $189.8175   $189.82   $189.80   $189.80  
  7 purchase totals = $847.37       $913.7058   $913.71   $913.70   $913.70