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 $9.35   6.790%   $9.9849   $9.98   $10.00   $10.00  
  Purchase #2 $227.94   9.342%   $249.2342   $249.23   $249.25   $249.20  
  Purchase #3 $38.56   12.639%   $43.4336   $43.43   $43.45   $43.40  
  Purchase #4 $194.70   9.827%   $213.8332   $213.83   $213.85   $213.80  
  Purchase #5 $63.43   9.426%   $69.4089   $69.41   $69.40   $69.40  
  Purchase #6 $183.96   7.615%   $197.9686   $197.97   $197.95   $198.00  
  Purchase #7 $142.91   8.382%   $154.8887   $154.89   $154.90   $154.90  
  7 purchase totals = $860.85       $938.7521   $938.74   $938.80   $938.70