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 $60.78   12.802%   $68.5611   $68.56   $68.55   $68.60  
  Purchase #2 $168.69   10.114%   $185.7513   $185.75   $185.75   $185.80  
  Purchase #3 $154.27   5.773%   $163.176   $163.18   $163.20   $163.20  
  Purchase #4 $156.36   7.189%   $167.6007   $167.60   $167.60   $167.60  
  Purchase #5 $220.73   8.123%   $238.6599   $238.66   $238.65   $238.70  
  Purchase #6 $39.46   6.346%   $41.9641   $41.96   $41.95   $42.00  
  Purchase #7 $226.79   4.749%   $237.5603   $237.56   $237.55   $237.60  
  7 purchase totals = $1,027.08       $1,103.2734   $1,103.27   $1,103.25   $1,103.50