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 $54.82   12.210%   $61.5135   $61.51   $61.50   $61.50  
  Purchase #2 $224.41   3.462%   $232.1791   $232.18   $232.20   $232.20  
  Purchase #3 $160.85   7.787%   $173.3754   $173.38   $173.40   $173.40  
  Purchase #4 $176.26   6.259%   $187.2921   $187.29   $187.30   $187.30  
  Purchase #5 $200.48   9.119%   $218.7618   $218.76   $218.75   $218.80  
  Purchase #6 $111.88   6.162%   $118.774   $118.77   $118.75   $118.80  
  Purchase #7 $224.99   11.874%   $251.7053   $251.71   $251.70   $251.70  
  7 purchase totals = $1,153.69       $1,243.6012   $1,243.60   $1,243.60   $1,243.70