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 $245.25   6.751%   $261.8068   $261.81   $261.80   $261.80  
  Purchase #2 $10.90   11.629%   $12.1676   $12.17   $12.15   $12.20  
  Purchase #3 $153.59   11.856%   $171.7996   $171.80   $171.80   $171.80  
  Purchase #4 $41.70   13.221%   $47.2132   $47.21   $47.20   $47.20  
  Purchase #5 $49.69   6.417%   $52.8786   $52.88   $52.90   $52.90  
  Purchase #6 $118.74   9.789%   $130.3635   $130.36   $130.35   $130.40  
  Purchase #7 $247.32   12.154%   $277.3793   $277.38   $277.40   $277.40  
  7 purchase totals = $867.19       $953.6086   $953.61   $953.60   $953.70