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 $195.99   13.117%   $221.698   $221.70   $221.70   $221.70  
  Purchase #2 $11.29   6.726%   $12.0494   $12.05   $12.05   $12.00  
  Purchase #3 $155.83   7.338%   $167.2648   $167.26   $167.25   $167.30  
  Purchase #4 $8.41   13.526%   $9.5475   $9.55   $9.55   $9.50  
  Purchase #5 $167.40   8.668%   $181.9102   $181.91   $181.90   $181.90  
  Purchase #6 $85.64   9.292%   $93.5977   $93.60   $93.60   $93.60  
  Purchase #7 $135.38   9.291%   $147.9582   $147.96   $147.95   $148.00  
  7 purchase totals = $759.94       $834.0258   $834.03   $834.00   $834.00