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 $210.53   11.786%   $235.3431   $235.34   $235.35   $235.30  
  Purchase #2 $101.49   13.806%   $115.5017   $115.50   $115.50   $115.50  
  Purchase #3 $135.72   11.738%   $151.6508   $151.65   $151.65   $151.70  
  Purchase #4 $192.36   6.540%   $204.9403   $204.94   $204.95   $204.90  
  Purchase #5 $64.26   11.824%   $71.8581   $71.86   $71.85   $71.90  
  Purchase #6 $86.35   9.429%   $94.4919   $94.49   $94.50   $94.50  
  Purchase #7 $151.73   4.248%   $158.1755   $158.18   $158.20   $158.20  
  7 purchase totals = $942.44       $1,031.9614   $1,031.96   $1,032.00   $1,032.00