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 $233.87   5.756%   $247.3316   $247.33   $247.35   $247.30  
  Purchase #2 $88.64   9.104%   $96.7098   $96.71   $96.70   $96.70  
  Purchase #3 $158.94   4.416%   $165.9588   $165.96   $165.95   $166.00  
  Purchase #4 $76.62   6.853%   $81.8708   $81.87   $81.85   $81.90  
  Purchase #5 $34.81   6.252%   $36.9863   $36.99   $37.00   $37.00  
  Purchase #6 $9.92   7.833%   $10.697   $10.70   $10.70   $10.70  
  Purchase #7 $196.29   13.238%   $222.2749   $222.27   $222.25   $222.30  
  7 purchase totals = $799.09       $861.8292   $861.83   $861.80   $861.90