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 $24.26   8.131%   $26.2326   $26.23   $26.25   $26.20  
  Purchase #2 $62.98   6.834%   $67.2841   $67.28   $67.30   $67.30  
  Purchase #3 $181.81   3.256%   $187.7297   $187.73   $187.75   $187.70  
  Purchase #4 $34.78   8.826%   $37.8497   $37.85   $37.85   $37.80  
  Purchase #5 $112.58   10.133%   $123.9877   $123.99   $124.00   $124.00  
  Purchase #6 $9.99   5.700%   $10.5594   $10.56   $10.55   $10.60  
  Purchase #7 $222.74   10.110%   $245.259   $245.26   $245.25   $245.30  
  7 purchase totals = $649.14       $698.9022   $698.90   $698.95   $698.90