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 $208.82   8.645%   $226.8725   $226.87   $226.85   $226.90  
  Purchase #2 $156.53   11.376%   $174.3369   $174.34   $174.35   $174.30  
  Purchase #3 $147.99   13.594%   $168.1078   $168.11   $168.10   $168.10  
  Purchase #4 $72.84   6.238%   $77.3838   $77.38   $77.40   $77.40  
  Purchase #5 $241.71   3.685%   $250.617   $250.62   $250.60   $250.60  
  Purchase #6 $107.94   9.806%   $118.5246   $118.52   $118.50   $118.50  
  Purchase #7 $183.52   6.504%   $195.4561   $195.46   $195.45   $195.50  
  7 purchase totals = $1,119.35       $1,211.2987   $1,211.30   $1,211.25   $1,211.30