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 $36.94   12.779%   $41.6606   $41.66   $41.65   $41.70  
  Purchase #2 $68.31   9.361%   $74.7045   $74.70   $74.70   $74.70  
  Purchase #3 $125.40   4.167%   $130.6254   $130.63   $130.65   $130.60  
  Purchase #4 $224.71   6.227%   $238.7027   $238.70   $238.70   $238.70  
  Purchase #5 $74.60   12.841%   $84.1794   $84.18   $84.20   $84.20  
  Purchase #6 $231.36   3.371%   $239.1591   $239.16   $239.15   $239.20  
  Purchase #7 $176.54   9.622%   $193.5267   $193.53   $193.55   $193.50  
  7 purchase totals = $937.86       $1,002.5584   $1,002.56   $1,002.60   $1,002.60