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 $217.25   11.282%   $241.7601   $241.76   $241.75   $241.80  
  Purchase #2 $177.50   11.164%   $197.3161   $197.32   $197.30   $197.30  
  Purchase #3 $240.68   8.498%   $261.133   $261.13   $261.15   $261.10  
  Purchase #4 $228.25   10.129%   $251.3694   $251.37   $251.35   $251.40  
  Purchase #5 $137.58   9.639%   $150.8413   $150.84   $150.85   $150.80  
  Purchase #6 $242.28   9.783%   $265.9823   $265.98   $266.00   $266.00  
  Purchase #7 $78.65   9.183%   $85.8724   $85.87   $85.85   $85.90  
  7 purchase totals = $1,322.19       $1,454.2746   $1,454.27   $1,454.25   $1,454.30