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 $38.62   13.747%   $43.9291   $43.93   $43.95   $43.90  
  Purchase #2 $249.32   6.305%   $265.0396   $265.04   $265.05   $265.00  
  Purchase #3 $74.49   4.329%   $77.7147   $77.71   $77.70   $77.70  
  Purchase #4 $167.38   6.661%   $178.5292   $178.53   $178.55   $178.50  
  Purchase #5 $171.32   4.130%   $178.3955   $178.40   $178.40   $178.40  
  Purchase #6 $190.39   8.418%   $206.417   $206.42   $206.40   $206.40  
  Purchase #7 $64.31   7.362%   $69.0445   $69.04   $69.05   $69.00  
  7 purchase totals = $955.83       $1,019.0696   $1,019.07   $1,019.10   $1,018.90