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 $192.37   7.737%   $207.2537   $207.25   $207.25   $207.30  
  Purchase #2 $12.29   12.112%   $13.7786   $13.78   $13.80   $13.80  
  Purchase #3 $59.55   4.365%   $62.1494   $62.15   $62.15   $62.10  
  Purchase #4 $165.85   6.661%   $176.8973   $176.90   $176.90   $176.90  
  Purchase #5 $175.95   5.197%   $185.0941   $185.09   $185.10   $185.10  
  Purchase #6 $44.97   8.668%   $48.868   $48.87   $48.85   $48.90  
  Purchase #7 $150.96   5.230%   $158.8552   $158.86   $158.85   $158.90  
  7 purchase totals = $801.94       $852.8963   $852.90   $852.90   $853.00