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 $244.68   7.334%   $262.6248   $262.62   $262.60   $262.60  
  Purchase #2 $23.64   12.737%   $26.651   $26.65   $26.65   $26.70  
  Purchase #3 $161.30   5.361%   $169.9473   $169.95   $169.95   $169.90  
  Purchase #4 $217.32   3.691%   $225.3413   $225.34   $225.35   $225.30  
  Purchase #5 $77.27   12.581%   $86.9913   $86.99   $87.00   $87.00  
  Purchase #6 $81.45   10.686%   $90.1537   $90.15   $90.15   $90.20  
  Purchase #7 $57.82   12.235%   $64.8943   $64.89   $64.90   $64.90  
  7 purchase totals = $863.48       $926.6037   $926.59   $926.60   $926.60