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 $85.63   12.226%   $96.0991   $96.10   $96.10   $96.10  
  Purchase #2 $96.69   9.179%   $105.5652   $105.57   $105.55   $105.60  
  Purchase #3 $159.84   5.538%   $168.6919   $168.69   $168.70   $168.70  
  Purchase #4 $15.93   6.683%   $16.9946   $16.99   $17.00   $17.00  
  Purchase #5 $71.55   3.738%   $74.2245   $74.22   $74.20   $74.20  
  Purchase #6 $240.59   10.285%   $265.3347   $265.33   $265.35   $265.30  
  Purchase #7 $211.65   7.419%   $227.3523   $227.35   $227.35   $227.40  
  7 purchase totals = $881.88       $954.2623   $954.25   $954.25   $954.30