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	$94.87	4.329%	$98.9769	$98.98	$99.00	$99.00
Purchase #2	$65.96	10.311%	$72.7611	$72.76	$72.75	$72.80
Purchase #3	$157.29	7.850%	$169.6373	$169.64	$169.65	$169.60
Purchase #4	$136.79	13.666%	$155.4837	$155.48	$155.50	$155.50
Purchase #5	$26.49	9.871%	$29.1048	$29.10	$29.10	$29.10
Purchase #6	$185.77	13.481%	$210.8137	$210.81	$210.80	$210.80
Purchase #7	$179.47	9.396%	$196.333	$196.33	$196.35	$196.30
7 purchase totals =	$846.64		$933.1105	$933.10	$933.15	$933.10