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 $71.87   10.733%   $79.5838   $79.58   $79.60   $79.60  
  Purchase #2 $248.39   11.699%   $277.4491   $277.45   $277.45   $277.40  
  Purchase #3 $204.71   13.734%   $232.8249   $232.82   $232.80   $232.80  
  Purchase #4 $172.72   7.367%   $185.4443   $185.44   $185.45   $185.40  
  Purchase #5 $220.59   7.448%   $237.0195   $237.02   $237.00   $237.00  
  Purchase #6 $75.28   10.185%   $82.9473   $82.95   $82.95   $82.90  
  Purchase #7 $244.41   11.258%   $271.9257   $271.93   $271.95   $271.90  
  7 purchase totals = $1,237.97       $1,367.1946   $1,367.19   $1,367.20   $1,367.00