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 $234.94   10.658%   $259.9799   $259.98   $260.00   $260.00  
  Purchase #2 $94.25   7.790%   $101.5921   $101.59   $101.60   $101.60  
  Purchase #3 $70.98   11.454%   $79.11   $79.11   $79.10   $79.10  
  Purchase #4 $203.30   8.136%   $219.8405   $219.84   $219.85   $219.80  
  Purchase #5 $101.53   13.565%   $115.3025   $115.30   $115.30   $115.30  
  Purchase #6 $70.93   11.703%   $79.2309   $79.23   $79.25   $79.20  
  Purchase #7 $28.99   5.269%   $30.5175   $30.52   $30.50   $30.50  
  7 purchase totals = $804.92       $885.5734   $885.57   $885.60   $885.50