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 $180.97   6.664%   $193.0298   $193.03   $193.05   $193.00  
  Purchase #2 $86.54   13.221%   $97.9815   $97.98   $98.00   $98.00  
  Purchase #3 $194.27   4.427%   $202.8703   $202.87   $202.85   $202.90  
  Purchase #4 $53.94   11.217%   $59.9904   $59.99   $60.00   $60.00  
  Purchase #5 $204.53   7.563%   $219.9986   $220.00   $220.00   $220.00  
  Purchase #6 $127.68   6.853%   $136.4299   $136.43   $136.45   $136.40  
  Purchase #7 $214.59   8.403%   $232.622   $232.62   $232.60   $232.60  
  7 purchase totals = $1,062.52       $1,142.9225   $1,142.92   $1,142.95   $1,142.90