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 $211.93   5.655%   $223.9146   $223.91   $223.90   $223.90  
  Purchase #2 $83.91   11.711%   $93.7367   $93.74   $93.75   $93.70  
  Purchase #3 $24.95   4.823%   $26.1533   $26.15   $26.15   $26.20  
  Purchase #4 $103.32   9.471%   $113.1054   $113.11   $113.10   $113.10  
  Purchase #5 $223.88   12.782%   $252.4963   $252.50   $252.50   $252.50  
  Purchase #6 $107.59   10.329%   $118.703   $118.70   $118.70   $118.70  
  Purchase #7 $241.74   9.721%   $265.2395   $265.24   $265.25   $265.20  
  7 purchase totals = $997.32       $1,093.3488   $1,093.35   $1,093.35   $1,093.30