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	$79.75	3.741%	$82.7334	$82.73	$82.75	$82.70
Purchase #2	$236.52	8.329%	$256.2198	$256.22	$256.20	$256.20
Purchase #3	$159.95	8.535%	$173.6017	$173.60	$173.60	$173.60
Purchase #4	$86.44	3.578%	$89.5328	$89.53	$89.55	$89.50
Purchase #5	$86.35	3.312%	$89.2099	$89.21	$89.20	$89.20
Purchase #6	$39.98	3.454%	$41.3609	$41.36	$41.35	$41.40
Purchase #7	$35.32	5.251%	$37.1747	$37.17	$37.15	$37.20
7 purchase totals =	$724.31		$769.8332	$769.82	$769.80	$769.80