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 $232.27   12.181%   $260.5628   $260.56   $260.55   $260.60  
  Purchase #2 $160.47   9.789%   $176.1784   $176.18   $176.20   $176.20  
  Purchase #3 $145.60   4.714%   $152.4636   $152.46   $152.45   $152.50  
  Purchase #4 $87.97   8.357%   $95.3217   $95.32   $95.30   $95.30  
  Purchase #5 $170.68   12.651%   $192.2727   $192.27   $192.25   $192.30  
  Purchase #6 $249.69   7.138%   $267.5129   $267.51   $267.50   $267.50  
  Purchase #7 $71.97   4.108%   $74.9265   $74.93   $74.95   $74.90  
  7 purchase totals = $1,118.65       $1,219.2386   $1,219.23   $1,219.20   $1,219.30