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 $178.59   4.164%   $186.0265   $186.03   $186.05   $186.00  
  Purchase #2 $245.54   7.232%   $263.2975   $263.30   $263.30   $263.30  
  Purchase #3 $46.42   8.227%   $50.239   $50.24   $50.25   $50.20  
  Purchase #4 $95.99   9.746%   $105.3452   $105.35   $105.35   $105.30  
  Purchase #5 $178.90   3.259%   $184.7304   $184.73   $184.75   $184.70  
  Purchase #6 $105.91   4.429%   $110.6008   $110.60   $110.60   $110.60  
  Purchase #7 $37.46   12.773%   $42.2448   $42.24   $42.25   $42.20  
  7 purchase totals = $888.81       $942.4842   $942.49   $942.55   $942.30