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 $88.85   3.181%   $91.6763   $91.68   $91.70   $91.70  
  Purchase #2 $153.94   12.866%   $173.7459   $173.75   $173.75   $173.70  
  Purchase #3 $128.80   6.147%   $136.7173   $136.72   $136.70   $136.70  
  Purchase #4 $119.92   13.870%   $136.5529   $136.55   $136.55   $136.60  
  Purchase #5 $5.39   4.134%   $5.6128   $5.61   $5.60   $5.60  
  Purchase #6 $133.56   8.338%   $144.6962   $144.70   $144.70   $144.70  
  Purchase #7 $244.38   7.495%   $262.6963   $262.70   $262.70   $262.70  
  7 purchase totals = $874.84       $951.6977   $951.71   $951.70   $951.70