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 $228.81   8.717%   $248.7554   $248.76   $248.75   $248.80  
  Purchase #2 $161.44   12.718%   $181.9719   $181.97   $181.95   $182.00  
  Purchase #3 $145.62   13.744%   $165.634   $165.63   $165.65   $165.60  
  Purchase #4 $233.61   9.665%   $256.1884   $256.19   $256.20   $256.20  
  Purchase #5 $232.99   8.698%   $253.2555   $253.26   $253.25   $253.30  
  Purchase #6 $148.37   8.427%   $160.8731   $160.87   $160.85   $160.90  
  Purchase #7 $64.70   8.128%   $69.9588   $69.96   $69.95   $70.00  
  7 purchase totals = $1,215.54       $1,336.6371   $1,336.64   $1,336.60   $1,336.80