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	$53.68	3.764%	$55.7005	$55.70	$55.70	$55.70
Purchase #2	$81.32	10.471%	$89.835	$89.84	$89.85	$89.80
Purchase #3	$72.63	6.254%	$77.1723	$77.17	$77.15	$77.20
Purchase #4	$153.52	3.507%	$158.9039	$158.90	$158.90	$158.90
Purchase #5	$171.88	6.698%	$183.3925	$183.39	$183.40	$183.40
Purchase #6	$102.53	3.713%	$106.3369	$106.34	$106.35	$106.30
Purchase #7	$159.48	8.446%	$172.9497	$172.95	$172.95	$172.90
7 purchase totals =	$795.04		$844.2908	$844.29	$844.30	$844.20