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 $154.86   8.361%   $167.8078   $167.81   $167.80   $167.80  
  Purchase #2 $60.39   13.149%   $68.3307   $68.33   $68.35   $68.30  
  Purchase #3 $111.50   11.594%   $124.4273   $124.43   $124.45   $124.40  
  Purchase #4 $159.34   10.709%   $176.4037   $176.40   $176.40   $176.40  
  Purchase #5 $109.96   8.664%   $119.4869   $119.49   $119.50   $119.50  
  Purchase #6 $233.43   13.689%   $265.3842   $265.38   $265.40   $265.40  
  Purchase #7 $195.87   12.606%   $220.5614   $220.56   $220.55   $220.60  
  7 purchase totals = $1,025.35       $1,142.4020   $1,142.40   $1,142.45   $1,142.40