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 $66.48   8.293%   $71.9932   $71.99   $72.00   $72.00  
  Purchase #2 $230.55   5.727%   $243.7536   $243.75   $243.75   $243.80  
  Purchase #3 $157.72   6.252%   $167.5807   $167.58   $167.60   $167.60  
  Purchase #4 $201.51   6.611%   $214.8318   $214.83   $214.85   $214.80  
  Purchase #5 $246.64   4.477%   $257.6821   $257.68   $257.70   $257.70  
  Purchase #6 $136.89   12.598%   $154.1354   $154.14   $154.15   $154.10  
  Purchase #7 $33.43   13.327%   $37.8852   $37.89   $37.90   $37.90  
  7 purchase totals = $1,073.22       $1,147.8620   $1,147.86   $1,147.95   $1,147.90