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 $172.44   6.565%   $183.7607   $183.76   $183.75   $183.80  
  Purchase #2 $109.43   3.826%   $113.6168   $113.62   $113.60   $113.60  
  Purchase #3 $205.26   6.402%   $218.4007   $218.40   $218.40   $218.40  
  Purchase #4 $227.94   12.837%   $257.2007   $257.20   $257.20   $257.20  
  Purchase #5 $189.51   9.309%   $207.1515   $207.15   $207.15   $207.20  
  Purchase #6 $182.44   12.114%   $204.5408   $204.54   $204.55   $204.50  
  Purchase #7 $178.78   4.392%   $186.632   $186.63   $186.65   $186.60  
  7 purchase totals = $1,265.80       $1,371.3032   $1,371.30   $1,371.30   $1,371.30