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 $232.66   12.342%   $261.3749   $261.37   $261.35   $261.40  
  Purchase #2 $83.26   10.197%   $91.75   $91.75   $91.75   $91.80  
  Purchase #3 $133.97   7.235%   $143.6627   $143.66   $143.65   $143.70  
  Purchase #4 $162.61   7.369%   $174.5927   $174.59   $174.60   $174.60  
  Purchase #5 $19.51   5.381%   $20.5598   $20.56   $20.55   $20.60  
  Purchase #6 $27.34   10.749%   $30.2788   $30.28   $30.30   $30.30  
  Purchase #7 $192.39   5.864%   $203.6717   $203.67   $203.65   $203.70  
  7 purchase totals = $851.74       $925.8906   $925.88   $925.85   $926.10