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 $247.93   5.506%   $261.581   $261.58   $261.60   $261.60  
  Purchase #2 $38.27   4.188%   $39.8727   $39.87   $39.85   $39.90  
  Purchase #3 $42.72   12.858%   $48.2129   $48.21   $48.20   $48.20  
  Purchase #4 $104.74   12.692%   $118.0336   $118.03   $118.05   $118.00  
  Purchase #5 $150.45   6.769%   $160.634   $160.63   $160.65   $160.60  
  Purchase #6 $23.26   11.721%   $25.9863   $25.99   $26.00   $26.00  
  Purchase #7 $230.94   9.313%   $252.4474   $252.45   $252.45   $252.40  
  7 purchase totals = $838.31       $906.7679   $906.76   $906.80   $906.70