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 $198.34   9.232%   $216.6507   $216.65   $216.65   $216.70  
  Purchase #2 $25.94   6.157%   $27.5371   $27.54   $27.55   $27.50  
  Purchase #3 $245.48   5.862%   $259.87   $259.87   $259.85   $259.90  
  Purchase #4 $84.85   4.155%   $88.3755   $88.38   $88.40   $88.40  
  Purchase #5 $58.38   13.623%   $66.3331   $66.33   $66.35   $66.30  
  Purchase #6 $113.94   10.797%   $126.2421   $126.24   $126.25   $126.20  
  Purchase #7 $250.99   12.593%   $282.5972   $282.60   $282.60   $282.60  
  7 purchase totals = $977.92       $1,067.6057   $1,067.61   $1,067.65   $1,067.60