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 $196.84   12.193%   $220.8407   $220.84   $220.85   $220.80  
  Purchase #2 $239.44   10.298%   $264.0975   $264.10   $264.10   $264.10  
  Purchase #3 $149.76   11.584%   $167.1082   $167.11   $167.10   $167.10  
  Purchase #4 $79.99   8.289%   $86.6204   $86.62   $86.60   $86.60  
  Purchase #5 $148.53   9.826%   $163.1246   $163.12   $163.10   $163.10  
  Purchase #6 $204.74   4.385%   $213.7178   $213.72   $213.70   $213.70  
  Purchase #7 $208.99   11.546%   $233.12   $233.12   $233.10   $233.10  
  7 purchase totals = $1,228.29       $1,348.6292   $1,348.63   $1,348.55   $1,348.50