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 $60.34   8.657%   $65.5636   $65.56   $65.55   $65.60  
  Purchase #2 $250.88   8.394%   $271.9389   $271.94   $271.95   $271.90  
  Purchase #3 $14.63   13.809%   $16.6503   $16.65   $16.65   $16.70  
  Purchase #4 $39.71   8.843%   $43.2216   $43.22   $43.20   $43.20  
  Purchase #5 $54.53   8.595%   $59.2169   $59.22   $59.20   $59.20  
  Purchase #6 $147.57   9.134%   $161.049   $161.05   $161.05   $161.00  
  Purchase #7 $232.33   7.128%   $248.8905   $248.89   $248.90   $248.90  
  7 purchase totals = $799.99       $866.5308   $866.53   $866.50   $866.50