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 $183.98   11.396%   $204.9464   $204.95   $204.95   $204.90  
  Purchase #2 $68.76   10.810%   $76.193   $76.19   $76.20   $76.20  
  Purchase #3 $245.86   3.124%   $253.5407   $253.54   $253.55   $253.50  
  Purchase #4 $95.44   3.574%   $98.851   $98.85   $98.85   $98.90  
  Purchase #5 $164.30   12.438%   $184.7356   $184.74   $184.75   $184.70  
  Purchase #6 $163.39   13.187%   $184.9362   $184.94   $184.95   $184.90  
  Purchase #7 $206.29   10.421%   $227.7875   $227.79   $227.80   $227.80  
  7 purchase totals = $1,128.02       $1,230.9904   $1,231.00   $1,231.05   $1,230.90