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 $169.32   13.731%   $192.5693   $192.57   $192.55   $192.60  
  Purchase #2 $237.52   5.294%   $250.0943   $250.09   $250.10   $250.10  
  Purchase #3 $151.83   11.522%   $169.3239   $169.32   $169.30   $169.30  
  Purchase #4 $59.76   6.868%   $63.8643   $63.86   $63.85   $63.90  
  Purchase #5 $206.76   5.371%   $217.8651   $217.87   $217.85   $217.90  
  Purchase #6 $196.57   8.627%   $213.5281   $213.53   $213.55   $213.50  
  Purchase #7 $14.90   13.754%   $16.9493   $16.95   $16.95   $16.90  
  7 purchase totals = $1,036.66       $1,124.1943   $1,124.19   $1,124.15   $1,124.20