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	$120.34	6.635%	$128.3246	$128.32	$128.30	$128.30
Purchase #2	$91.86	7.677%	$98.9121	$98.91	$98.90	$98.90
Purchase #3	$35.47	10.287%	$39.1188	$39.12	$39.10	$39.10
Purchase #4	$172.36	12.217%	$193.4172	$193.42	$193.40	$193.40
Purchase #5	$45.42	10.157%	$50.0333	$50.03	$50.05	$50.00
Purchase #6	$80.54	7.530%	$86.6047	$86.60	$86.60	$86.60
Purchase #7	$165.26	4.617%	$172.8901	$172.89	$172.90	$172.90
7 purchase totals =	$711.25		$769.3008	$769.29	$769.25	$769.20