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 $87.55   12.205%   $98.2355   $98.24   $98.25   $98.20  
  Purchase #2 $30.62   13.192%   $34.6594   $34.66   $34.65   $34.70  
  Purchase #3 $85.25   13.741%   $96.9642   $96.96   $96.95   $97.00  
  Purchase #4 $62.80   7.639%   $67.5973   $67.60   $67.60   $67.60  
  Purchase #5 $113.79   3.576%   $117.8591   $117.86   $117.85   $117.90  
  Purchase #6 $137.77   12.133%   $154.4856   $154.49   $154.50   $154.50  
  Purchase #7 $114.71   11.748%   $128.1861   $128.19   $128.20   $128.20  
  7 purchase totals = $632.49       $697.9872   $698.00   $698.00   $698.10