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 $171.95   7.422%   $184.7121   $184.71   $184.70   $184.70  
  Purchase #2 $53.94   9.373%   $58.9958   $59.00   $59.00   $59.00  
  Purchase #3 $186.80   7.174%   $200.201   $200.20   $200.20   $200.20  
  Purchase #4 $162.31   3.745%   $168.3885   $168.39   $168.40   $168.40  
  Purchase #5 $187.43   11.453%   $208.8964   $208.90   $208.90   $208.90  
  Purchase #6 $110.62   3.318%   $114.2904   $114.29   $114.30   $114.30  
  Purchase #7 $108.48   13.353%   $122.9653   $122.97   $122.95   $123.00  
  7 purchase totals = $981.53       $1,058.4495   $1,058.46   $1,058.45   $1,058.50