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 $175.53   5.479%   $185.1473   $185.15   $185.15   $185.10  
  Purchase #2 $15.92   6.811%   $17.0043   $17.00   $17.00   $17.00  
  Purchase #3 $204.27   13.485%   $231.8158   $231.82   $231.80   $231.80  
  Purchase #4 $135.55   5.148%   $142.5281   $142.53   $142.55   $142.50  
  Purchase #5 $213.73   9.529%   $234.0963   $234.10   $234.10   $234.10  
  Purchase #6 $130.93   6.635%   $139.6172   $139.62   $139.60   $139.60  
  Purchase #7 $11.45   5.702%   $12.1029   $12.10   $12.10   $12.10  
  7 purchase totals = $887.38       $962.3119   $962.32   $962.30   $962.20