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 $44.70   6.395%   $47.5586   $47.56   $47.55   $47.60  
  Purchase #2 $136.64   12.177%   $153.2787   $153.28   $153.30   $153.30  
  Purchase #3 $153.64   6.762%   $164.0291   $164.03   $164.05   $164.00  
  Purchase #4 $203.70   9.683%   $223.4243   $223.42   $223.40   $223.40  
  Purchase #5 $233.69   4.186%   $243.4723   $243.47   $243.45   $243.50  
  Purchase #6 $168.73   11.213%   $187.6497   $187.65   $187.65   $187.60  
  Purchase #7 $111.95   11.211%   $124.5007   $124.50   $124.50   $124.50  
  7 purchase totals = $1,053.05       $1,143.9134   $1,143.91   $1,143.90   $1,143.90