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 $176.33   13.543%   $200.2104   $200.21   $200.20   $200.20  
  Purchase #2 $231.95   9.226%   $253.3497   $253.35   $253.35   $253.30  
  Purchase #3 $226.65   3.461%   $234.4944   $234.49   $234.50   $234.50  
  Purchase #4 $197.56   12.702%   $222.6541   $222.65   $222.65   $222.70  
  Purchase #5 $113.70   5.305%   $119.7318   $119.73   $119.75   $119.70  
  Purchase #6 $89.94   9.132%   $98.1533   $98.15   $98.15   $98.20  
  Purchase #7 $209.88   11.313%   $233.6237   $233.62   $233.60   $233.60  
  7 purchase totals = $1,246.01       $1,362.2174   $1,362.20   $1,362.20   $1,362.20