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 $60.82   9.773%   $66.7639   $66.76   $66.75   $66.80  
  Purchase #2 $25.83   8.115%   $27.9261   $27.93   $27.95   $27.90  
  Purchase #3 $101.44   13.197%   $114.827   $114.83   $114.85   $114.80  
  Purchase #4 $162.66   6.365%   $173.0133   $173.01   $173.00   $173.00  
  Purchase #5 $120.69   11.424%   $134.4776   $134.48   $134.50   $134.50  
  Purchase #6 $176.34   13.546%   $200.227   $200.23   $200.25   $200.20  
  Purchase #7 $175.45   10.453%   $193.7898   $193.79   $193.80   $193.80  
  7 purchase totals = $823.23       $911.0247   $911.03   $911.10   $911.00