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 $219.40   9.847%   $241.0043   $241.00   $241.00   $241.00  
  Purchase #2 $21.56   5.753%   $22.8003   $22.80   $22.80   $22.80  
  Purchase #3 $161.44   7.552%   $173.6319   $173.63   $173.65   $173.60  
  Purchase #4 $135.68   9.266%   $148.2521   $148.25   $148.25   $148.30  
  Purchase #5 $176.98   11.500%   $197.3327   $197.33   $197.35   $197.30  
  Purchase #6 $153.39   9.705%   $168.2765   $168.28   $168.30   $168.30  
  Purchase #7 $238.90   4.730%   $250.2   $250.20   $250.20   $250.20  
  7 purchase totals = $1,107.35       $1,201.4978   $1,201.49   $1,201.55   $1,201.50