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	$46.83	8.660%	$50.8855	$50.89	$50.90	$50.90
Purchase #2	$24.42	11.171%	$27.148	$27.15	$27.15	$27.10
Purchase #3	$236.90	3.352%	$244.8409	$244.84	$244.85	$244.80
Purchase #4	$153.82	11.353%	$171.2832	$171.28	$171.30	$171.30
Purchase #5	$188.49	9.542%	$206.4757	$206.48	$206.50	$206.50
Purchase #6	$144.69	3.872%	$150.2924	$150.29	$150.30	$150.30
Purchase #7	$88.31	7.247%	$94.7098	$94.71	$94.70	$94.70
7 purchase totals =	$883.46		$945.6355	$945.64	$945.70	$945.60