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 $206.36   13.704%   $234.6396   $234.64   $234.65   $234.60  
  Purchase #2 $208.29   6.458%   $221.7414   $221.74   $221.75   $221.70  
  Purchase #3 $172.83   10.248%   $190.5416   $190.54   $190.55   $190.50  
  Purchase #4 $230.96   6.328%   $245.5751   $245.58   $245.60   $245.60  
  Purchase #5 $150.73   10.440%   $166.4662   $166.47   $166.45   $166.50  
  Purchase #6 $161.92   13.170%   $183.2449   $183.24   $183.25   $183.20  
  Purchase #7 $72.35   4.317%   $75.4733   $75.47   $75.45   $75.50  
  7 purchase totals = $1,203.44       $1,317.6821   $1,317.68   $1,317.70   $1,317.60