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 $151.37   8.177%   $163.7475   $163.75   $163.75   $163.70  
  Purchase #2 $205.49   4.139%   $213.9952   $214.00   $214.00   $214.00  
  Purchase #3 $8.82   4.331%   $9.202   $9.20   $9.20   $9.20  
  Purchase #4 $146.45   4.257%   $152.6844   $152.68   $152.70   $152.70  
  Purchase #5 $59.42   12.587%   $66.8992   $66.90   $66.90   $66.90  
  Purchase #6 $166.57   7.156%   $178.4897   $178.49   $178.50   $178.50  
  Purchase #7 $233.73   13.598%   $265.5126   $265.51   $265.50   $265.50  
  7 purchase totals = $971.85       $1,050.5306   $1,050.53   $1,050.55   $1,050.50