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 $185.93   11.316%   $206.9698   $206.97   $206.95   $207.00  
  Purchase #2 $91.78   3.542%   $95.0308   $95.03   $95.05   $95.00  
  Purchase #3 $66.88   6.251%   $71.0607   $71.06   $71.05   $71.10  
  Purchase #4 $56.66   10.631%   $62.6835   $62.68   $62.70   $62.70  
  Purchase #5 $149.29   13.174%   $168.9575   $168.96   $168.95   $169.00  
  Purchase #6 $117.91   13.265%   $133.5508   $133.55   $133.55   $133.60  
  Purchase #7 $123.95   5.313%   $130.5355   $130.54   $130.55   $130.50  
  7 purchase totals = $792.40       $868.7886   $868.79   $868.80   $868.90