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 $60.65   9.330%   $66.3086   $66.31   $66.30   $66.30  
  Purchase #2 $183.81   10.300%   $202.7424   $202.74   $202.75   $202.70  
  Purchase #3 $101.82   12.410%   $114.4559   $114.46   $114.45   $114.50  
  Purchase #4 $92.71   6.483%   $98.7204   $98.72   $98.70   $98.70  
  Purchase #5 $12.40   6.497%   $13.2056   $13.21   $13.20   $13.20  
  Purchase #6 $238.74   8.783%   $259.7085   $259.71   $259.70   $259.70  
  Purchase #7 $224.90   12.290%   $252.5402   $252.54   $252.55   $252.50  
  7 purchase totals = $915.03       $1,007.6816   $1,007.69   $1,007.65   $1,007.60