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 $114.33   13.248%   $129.4764   $129.48   $129.50   $129.50  
  Purchase #2 $60.41   3.795%   $62.7026   $62.70   $62.70   $62.70  
  Purchase #3 $127.62   3.226%   $131.737   $131.74   $131.75   $131.70  
  Purchase #4 $228.66   3.452%   $236.5533   $236.55   $236.55   $236.60  
  Purchase #5 $118.64   7.694%   $127.7682   $127.77   $127.75   $127.80  
  Purchase #6 $153.55   10.287%   $169.3457   $169.35   $169.35   $169.30  
  Purchase #7 $122.78   12.389%   $137.9912   $137.99   $138.00   $138.00  
  7 purchase totals = $925.99       $995.5744   $995.58   $995.60   $995.60