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 $204.79   8.228%   $221.6401   $221.64   $221.65   $221.60  
  Purchase #2 $96.57   10.704%   $106.9069   $106.91   $106.90   $106.90  
  Purchase #3 $13.31   7.412%   $14.2965   $14.30   $14.30   $14.30  
  Purchase #4 $41.64   9.654%   $45.6599   $45.66   $45.65   $45.70  
  Purchase #5 $34.66   10.310%   $38.2334   $38.23   $38.25   $38.20  
  Purchase #6 $223.47   11.381%   $248.9031   $248.90   $248.90   $248.90  
  Purchase #7 $21.76   4.854%   $22.8162   $22.82   $22.80   $22.80  
  7 purchase totals = $636.20       $698.4561   $698.46   $698.45   $698.40