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 $213.35   8.128%   $230.6911   $230.69   $230.70   $230.70  
  Purchase #2 $134.89   4.376%   $140.7928   $140.79   $140.80   $140.80  
  Purchase #3 $56.67   13.616%   $64.3862   $64.39   $64.40   $64.40  
  Purchase #4 $218.89   9.274%   $239.1899   $239.19   $239.20   $239.20  
  Purchase #5 $116.92   12.649%   $131.7092   $131.71   $131.70   $131.70  
  Purchase #6 $187.76   6.318%   $199.6227   $199.62   $199.60   $199.60  
  Purchase #7 $60.49   8.214%   $65.4586   $65.46   $65.45   $65.50  
  7 purchase totals = $988.97       $1,071.8505   $1,071.85   $1,071.85   $1,071.90