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 $22.66   13.672%   $25.7581   $25.76   $25.75   $25.80  
  Purchase #2 $225.41   4.301%   $235.1049   $235.10   $235.10   $235.10  
  Purchase #3 $86.67   6.163%   $92.0115   $92.01   $92.00   $92.00  
  Purchase #4 $138.81   11.812%   $155.2062   $155.21   $155.20   $155.20  
  Purchase #5 $206.74   3.410%   $213.7898   $213.79   $213.80   $213.80  
  Purchase #6 $248.29   10.834%   $275.1897   $275.19   $275.20   $275.20  
  Purchase #7 $50.44   4.354%   $52.6362   $52.64   $52.65   $52.60  
  7 purchase totals = $979.02       $1,049.6964   $1,049.70   $1,049.70   $1,049.70