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	$35.62	6.436%	$37.9125	$37.91	$37.90	$37.90
Purchase #2	$64.46	10.488%	$71.2206	$71.22	$71.20	$71.20
Purchase #3	$147.67	11.575%	$164.7628	$164.76	$164.75	$164.80
Purchase #4	$50.36	5.874%	$53.3181	$53.32	$53.30	$53.30
Purchase #5	$102.57	3.292%	$105.9466	$105.95	$105.95	$105.90
Purchase #6	$166.91	3.359%	$172.5165	$172.52	$172.50	$172.50
Purchase #7	$211.39	11.593%	$235.8964	$235.90	$235.90	$235.90
7 purchase totals =	$778.98		$841.5735	$841.58	$841.50	$841.50