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 $33.59   8.757%   $36.5315   $36.53   $36.55   $36.50  
  Purchase #2 $159.77   10.285%   $176.2023   $176.20   $176.20   $176.20  
  Purchase #3 $205.43   12.782%   $231.6881   $231.69   $231.70   $231.70  
  Purchase #4 $249.88   8.471%   $271.0473   $271.05   $271.05   $271.00  
  Purchase #5 $245.89   5.470%   $259.3402   $259.34   $259.35   $259.30  
  Purchase #6 $224.48   10.495%   $248.0392   $248.04   $248.05   $248.00  
  Purchase #7 $235.29   11.449%   $262.2284   $262.23   $262.25   $262.20  
  7 purchase totals = $1,354.33       $1,485.0770   $1,485.08   $1,485.15   $1,484.90