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 $53.96   11.264%   $60.0381   $60.04   $60.05   $60.00  
  Purchase #2 $128.28   3.242%   $132.4388   $132.44   $132.45   $132.40  
  Purchase #3 $59.68   11.432%   $66.5026   $66.50   $66.50   $66.50  
  Purchase #4 $218.70   5.163%   $229.9915   $229.99   $230.00   $230.00  
  Purchase #5 $162.73   9.479%   $178.1552   $178.16   $178.15   $178.20  
  Purchase #6 $83.61   13.488%   $94.8873   $94.89   $94.90   $94.90  
  Purchase #7 $241.61   4.266%   $251.9171   $251.92   $251.90   $251.90  
  7 purchase totals = $948.57       $1,013.9306   $1,013.94   $1,013.95   $1,013.90