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 $44.68   13.556%   $50.7368   $50.74   $50.75   $50.70  
  Purchase #2 $154.81   8.269%   $167.6112   $167.61   $167.60   $167.60  
  Purchase #3 $151.82   3.233%   $156.7283   $156.73   $156.75   $156.70  
  Purchase #4 $207.64   12.331%   $233.2441   $233.24   $233.25   $233.20  
  Purchase #5 $80.33   13.532%   $91.2003   $91.20   $91.20   $91.20  
  Purchase #6 $201.64   5.620%   $212.9722   $212.97   $212.95   $213.00  
  Purchase #7 $84.60   9.739%   $92.8392   $92.84   $92.85   $92.80  
  7 purchase totals = $925.52       $1,005.3321   $1,005.33   $1,005.35   $1,005.20