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 $178.51   8.115%   $192.9961   $193.00   $193.00   $193.00  
  Purchase #2 $216.86   11.378%   $241.5343   $241.53   $241.55   $241.50  
  Purchase #3 $32.88   10.738%   $36.4107   $36.41   $36.40   $36.40  
  Purchase #4 $16.43   7.405%   $17.6466   $17.65   $17.65   $17.60  
  Purchase #5 $17.31   4.271%   $18.0493   $18.05   $18.05   $18.00  
  Purchase #6 $195.51   3.334%   $202.0283   $202.03   $202.05   $202.00  
  Purchase #7 $113.61   12.141%   $127.4034   $127.40   $127.40   $127.40  
  7 purchase totals = $771.11       $836.0687   $836.07   $836.10   $835.90