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 $232.42   11.122%   $258.2698   $258.27   $258.25   $258.30  
  Purchase #2 $244.89   11.313%   $272.5944   $272.59   $272.60   $272.60  
  Purchase #3 $152.29   10.818%   $168.7647   $168.76   $168.75   $168.80  
  Purchase #4 $211.90   5.116%   $222.7408   $222.74   $222.75   $222.70  
  Purchase #5 $129.90   8.467%   $140.8986   $140.90   $140.90   $140.90  
  Purchase #6 $161.45   8.401%   $175.0134   $175.01   $175.00   $175.00  
  Purchase #7 $92.37   5.848%   $97.7718   $97.77   $97.75   $97.80  
  7 purchase totals = $1,225.22       $1,336.0535   $1,336.04   $1,336.00   $1,336.10