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 $34.27   12.152%   $38.4345   $38.43   $38.45   $38.40  
  Purchase #2 $177.86   8.271%   $192.5708   $192.57   $192.55   $192.60  
  Purchase #3 $240.95   10.543%   $266.3534   $266.35   $266.35   $266.40  
  Purchase #4 $209.86   4.463%   $219.2261   $219.23   $219.25   $219.20  
  Purchase #5 $71.27   9.320%   $77.9124   $77.91   $77.90   $77.90  
  Purchase #6 $127.50   3.696%   $132.2124   $132.21   $132.20   $132.20  
  Purchase #7 $156.33   12.650%   $176.1057   $176.11   $176.10   $176.10  
  7 purchase totals = $1,018.04       $1,102.8153   $1,102.81   $1,102.80   $1,102.80