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	$92.93	11.695%	$103.7982	$103.80	$103.80	$103.80
Purchase #2	$83.65	6.739%	$89.2872	$89.29	$89.30	$89.30
Purchase #3	$237.31	9.694%	$260.3148	$260.31	$260.30	$260.30
Purchase #4	$231.83	5.441%	$244.4439	$244.44	$244.45	$244.40
Purchase #5	$139.97	7.196%	$150.0422	$150.04	$150.05	$150.00
Purchase #6	$157.26	11.162%	$174.8134	$174.81	$174.80	$174.80
Purchase #7	$24.90	12.268%	$27.9547	$27.95	$27.95	$28.00
7 purchase totals =	$967.85		$1,050.6544	$1,050.64	$1,050.65	$1,050.60