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 $114.33   12.415%   $128.5241   $128.52   $128.50   $128.50  
  Purchase #2 $12.55   13.117%   $14.1962   $14.20   $14.20   $14.20  
  Purchase #3 $48.60   9.331%   $53.1349   $53.13   $53.15   $53.10  
  Purchase #4 $168.28   13.730%   $191.3848   $191.38   $191.40   $191.40  
  Purchase #5 $182.32   10.383%   $201.2503   $201.25   $201.25   $201.30  
  Purchase #6 $244.97   6.624%   $261.1968   $261.20   $261.20   $261.20  
  Purchase #7 $162.88   13.438%   $184.7678   $184.77   $184.75   $184.80  
  7 purchase totals = $933.93       $1,034.4549   $1,034.45   $1,034.45   $1,034.50