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 $172.84   6.622%   $184.2855   $184.29   $184.30   $184.30  
  Purchase #2 $11.27   12.450%   $12.6731   $12.67   $12.65   $12.70  
  Purchase #3 $214.98   7.406%   $230.9014   $230.90   $230.90   $230.90  
  Purchase #4 $223.32   10.218%   $246.1388   $246.14   $246.15   $246.10  
  Purchase #5 $134.71   6.345%   $143.2573   $143.26   $143.25   $143.30  
  Purchase #6 $172.73   9.361%   $188.8993   $188.90   $188.90   $188.90  
  Purchase #7 $7.63   10.459%   $8.428   $8.43   $8.45   $8.40  
  7 purchase totals = $937.48       $1,014.5834   $1,014.59   $1,014.60   $1,014.60