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 $209.68   11.376%   $233.5332   $233.53   $233.55   $233.50  
  Purchase #2 $185.43   10.325%   $204.5756   $204.58   $204.60   $204.60  
  Purchase #3 $115.75   7.413%   $124.3305   $124.33   $124.35   $124.30  
  Purchase #4 $215.66   12.453%   $242.5161   $242.52   $242.50   $242.50  
  Purchase #5 $161.36   3.441%   $166.9124   $166.91   $166.90   $166.90  
  Purchase #6 $213.70   9.314%   $233.604   $233.60   $233.60   $233.60  
  Purchase #7 $21.78   11.235%   $24.227   $24.23   $24.25   $24.20  
  7 purchase totals = $1,123.36       $1,229.6988   $1,229.70   $1,229.75   $1,229.60