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 $243.30   9.176%   $265.6252   $265.63   $265.65   $265.60  
  Purchase #2 $123.91   8.862%   $134.8909   $134.89   $134.90   $134.90  
  Purchase #3 $38.29   12.547%   $43.0942   $43.09   $43.10   $43.10  
  Purchase #4 $231.97   5.278%   $244.2134   $244.21   $244.20   $244.20  
  Purchase #5 $230.36   13.442%   $261.325   $261.33   $261.35   $261.30  
  Purchase #6 $141.41   10.707%   $156.5508   $156.55   $156.55   $156.60  
  Purchase #7 $139.64   11.212%   $155.2964   $155.30   $155.30   $155.30  
  7 purchase totals = $1,148.88       $1,260.9959   $1,261.00   $1,261.05   $1,261.00