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	$70.64	11.407%	$78.6979	$78.70	$78.70	$78.70
Purchase #2	$248.63	6.296%	$264.2837	$264.28	$264.30	$264.30
Purchase #3	$56.71	13.235%	$64.2156	$64.22	$64.20	$64.20
Purchase #4	$52.31	6.175%	$55.5401	$55.54	$55.55	$55.50
Purchase #5	$20.73	3.108%	$21.3743	$21.37	$21.35	$21.40
Purchase #6	$139.41	9.147%	$152.1618	$152.16	$152.15	$152.20
Purchase #7	$154.56	8.804%	$168.1675	$168.17	$168.15	$168.20
7 purchase totals =	$742.99		$804.4409	$804.44	$804.40	$804.50