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 $157.50   6.146%   $167.18   $167.18   $167.20   $167.20  
  Purchase #2 $51.42   6.266%   $54.642   $54.64   $54.65   $54.60  
  Purchase #3 $228.47   9.408%   $249.9645   $249.96   $249.95   $250.00  
  Purchase #4 $16.78   3.533%   $17.3728   $17.37   $17.35   $17.40  
  Purchase #5 $52.98   8.627%   $57.5506   $57.55   $57.55   $57.60  
  Purchase #6 $153.69   6.669%   $163.9396   $163.94   $163.95   $163.90  
  Purchase #7 $193.34   9.798%   $212.2835   $212.28   $212.30   $212.30  
  7 purchase totals = $854.18       $922.9330   $922.92   $922.95   $923.00