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 $248.52   5.763%   $262.8422   $262.84   $262.85   $262.80  
  Purchase #2 $56.71   12.436%   $63.7625   $63.76   $63.75   $63.80  
  Purchase #3 $114.70   11.765%   $128.1945   $128.19   $128.20   $128.20  
  Purchase #4 $138.65   6.350%   $147.4543   $147.45   $147.45   $147.50  
  Purchase #5 $57.93   8.104%   $62.6246   $62.62   $62.60   $62.60  
  Purchase #6 $186.50   12.205%   $209.2623   $209.26   $209.25   $209.30  
  Purchase #7 $76.59   6.685%   $81.71   $81.71   $81.70   $81.70  
  7 purchase totals = $879.60       $955.8504   $955.83   $955.80   $955.90