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 $130.50   7.200%   $139.896   $139.90   $139.90   $139.90  
  Purchase #2 $173.48   6.287%   $184.3867   $184.39   $184.40   $184.40  
  Purchase #3 $9.37   8.708%   $10.1859   $10.19   $10.20   $10.20  
  Purchase #4 $75.64   8.436%   $82.021   $82.02   $82.00   $82.00  
  Purchase #5 $33.74   4.606%   $35.2941   $35.29   $35.30   $35.30  
  Purchase #6 $43.81   5.349%   $46.1534   $46.15   $46.15   $46.20  
  Purchase #7 $131.80   10.127%   $145.1474   $145.15   $145.15   $145.10  
  7 purchase totals = $598.34       $643.0845   $643.09   $643.10   $643.10