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 $130.25   3.260%   $134.4962   $134.50   $134.50   $134.50  
  Purchase #2 $85.87   10.317%   $94.7292   $94.73   $94.75   $94.70  
  Purchase #3 $214.81   11.820%   $240.2005   $240.20   $240.20   $240.20  
  Purchase #4 $162.48   4.366%   $169.5739   $169.57   $169.55   $169.60  
  Purchase #5 $59.84   6.829%   $63.9265   $63.93   $63.95   $63.90  
  Purchase #6 $208.94   13.869%   $237.9179   $237.92   $237.90   $237.90  
  Purchase #7 $215.54   11.701%   $240.7603   $240.76   $240.75   $240.80  
  7 purchase totals = $1,077.73       $1,181.6045   $1,181.61   $1,181.60   $1,181.60