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 $179.61   8.133%   $194.2177   $194.22   $194.20   $194.20  
  Purchase #2 $5.92   3.269%   $6.1135   $6.11   $6.10   $6.10  
  Purchase #3 $38.63   12.571%   $43.4862   $43.49   $43.50   $43.50  
  Purchase #4 $125.41   13.280%   $142.0644   $142.06   $142.05   $142.10  
  Purchase #5 $220.71   4.519%   $230.6839   $230.68   $230.70   $230.70  
  Purchase #6 $169.75   4.103%   $176.7148   $176.71   $176.70   $176.70  
  Purchase #7 $56.92   12.268%   $63.9029   $63.90   $63.90   $63.90  
  7 purchase totals = $796.95       $857.1834   $857.17   $857.15   $857.20