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 $109.52   13.852%   $124.6907   $124.69   $124.70   $124.70  
  Purchase #2 $40.53   13.363%   $45.946   $45.95   $45.95   $45.90  
  Purchase #3 $199.76   6.285%   $212.3149   $212.31   $212.30   $212.30  
  Purchase #4 $159.33   9.291%   $174.1334   $174.13   $174.15   $174.10  
  Purchase #5 $58.53   9.133%   $63.8755   $63.88   $63.90   $63.90  
  Purchase #6 $179.25   3.746%   $185.9647   $185.96   $185.95   $186.00  
  Purchase #7 $92.27   6.268%   $98.0535   $98.05   $98.05   $98.10  
  7 purchase totals = $839.19       $904.9787   $904.97   $905.00   $905.00