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	$164.99	4.234%	$171.9757	$171.98	$172.00	$172.00
Purchase #2	$91.47	13.199%	$103.5431	$103.54	$103.55	$103.50
Purchase #3	$215.83	3.769%	$223.9646	$223.96	$223.95	$224.00
Purchase #4	$83.57	4.479%	$87.3131	$87.31	$87.30	$87.30
Purchase #5	$21.56	3.524%	$22.3198	$22.32	$22.30	$22.30
Purchase #6	$59.53	8.660%	$64.6853	$64.69	$64.70	$64.70
Purchase #7	$90.37	11.655%	$100.9026	$100.90	$100.90	$100.90
7 purchase totals =	$727.32		$774.7042	$774.70	$774.70	$774.70