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 $80.33   5.744%   $84.9442   $84.94   $84.95   $84.90  
  Purchase #2 $53.62   12.739%   $60.4507   $60.45   $60.45   $60.50  
  Purchase #3 $184.91   8.708%   $201.012   $201.01   $201.00   $201.00  
  Purchase #4 $48.76   3.669%   $50.549   $50.55   $50.55   $50.50  
  Purchase #5 $208.97   4.791%   $218.9818   $218.98   $219.00   $219.00  
  Purchase #6 $165.97   9.246%   $181.3156   $181.32   $181.30   $181.30  
  Purchase #7 $194.50   10.117%   $214.1776   $214.18   $214.20   $214.20  
  7 purchase totals = $937.06       $1,011.4309   $1,011.43   $1,011.45   $1,011.40