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 $68.43   10.465%   $75.5912   $75.59   $75.60   $75.60  
  Purchase #2 $97.75   5.437%   $103.0647   $103.06   $103.05   $103.10  
  Purchase #3 $113.40   4.632%   $118.6527   $118.65   $118.65   $118.70  
  Purchase #4 $115.94   7.251%   $124.3468   $124.35   $124.35   $124.30  
  Purchase #5 $11.65   8.185%   $12.6036   $12.60   $12.60   $12.60  
  Purchase #6 $175.52   8.602%   $190.6182   $190.62   $190.60   $190.60  
  Purchase #7 $168.99   13.124%   $191.1682   $191.17   $191.15   $191.20  
  7 purchase totals = $751.68       $816.0454   $816.04   $816.00   $816.10