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 $9.74   7.107%   $10.4322   $10.43   $10.45   $10.40  
  Purchase #2 $114.32   13.573%   $129.8367   $129.84   $129.85   $129.80  
  Purchase #3 $11.99   12.280%   $13.4624   $13.46   $13.45   $13.50  
  Purchase #4 $20.63   7.669%   $22.2121   $22.21   $22.20   $22.20  
  Purchase #5 $152.41   7.183%   $163.3576   $163.36   $163.35   $163.40  
  Purchase #6 $153.91   6.200%   $163.4524   $163.45   $163.45   $163.50  
  Purchase #7 $117.74   4.122%   $122.5932   $122.59   $122.60   $122.60  
  7 purchase totals = $580.74       $625.3466   $625.34   $625.35   $625.40