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 $54.77   8.129%   $59.2223   $59.22   $59.20   $59.20  
  Purchase #2 $94.44   5.535%   $99.6673   $99.67   $99.65   $99.70  
  Purchase #3 $178.37   9.226%   $194.8264   $194.83   $194.85   $194.80  
  Purchase #4 $235.49   6.679%   $251.2184   $251.22   $251.20   $251.20  
  Purchase #5 $248.25   5.304%   $261.4172   $261.42   $261.40   $261.40  
  Purchase #6 $222.34   4.784%   $232.9767   $232.98   $233.00   $233.00  
  Purchase #7 $50.25   4.378%   $52.4499   $52.45   $52.45   $52.40  
  7 purchase totals = $1,083.91       $1,151.7782   $1,151.79   $1,151.75   $1,151.70