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 $23.97   9.699%   $26.2949   $26.29   $26.30   $26.30  
  Purchase #2 $77.45   12.219%   $86.9136   $86.91   $86.90   $86.90  
  Purchase #3 $148.61   12.312%   $166.9069   $166.91   $166.90   $166.90  
  Purchase #4 $186.35   4.804%   $195.3023   $195.30   $195.30   $195.30  
  Purchase #5 $121.88   9.619%   $133.6036   $133.60   $133.60   $133.60  
  Purchase #6 $221.50   11.301%   $246.5317   $246.53   $246.55   $246.50  
  Purchase #7 $198.87   12.462%   $223.6532   $223.65   $223.65   $223.70  
  7 purchase totals = $978.63       $1,079.2062   $1,079.19   $1,079.20   $1,079.20