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	$35.39	11.261%	$39.3753	$39.38	$39.40	$39.40
Purchase #2	$194.34	7.459%	$208.8358	$208.84	$208.85	$208.80
Purchase #3	$144.34	4.327%	$150.5856	$150.59	$150.60	$150.60
Purchase #4	$215.88	10.148%	$237.7875	$237.79	$237.80	$237.80
Purchase #5	$160.32	3.786%	$166.3897	$166.39	$166.40	$166.40
Purchase #6	$55.59	7.700%	$59.8704	$59.87	$59.85	$59.90
Purchase #7	$59.49	5.753%	$62.9125	$62.91	$62.90	$62.90
7 purchase totals =	$865.35		$925.7568	$925.77	$925.80	$925.80