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	$242.82	8.530%	$263.5325	$263.53	$263.55	$263.50
Purchase #2	$184.75	13.361%	$209.4344	$209.43	$209.45	$209.40
Purchase #3	$203.69	9.615%	$223.2748	$223.27	$223.25	$223.30
Purchase #4	$164.94	9.530%	$180.6588	$180.66	$180.65	$180.70
Purchase #5	$186.31	5.280%	$196.1472	$196.15	$196.15	$196.10
Purchase #6	$129.36	8.807%	$140.7527	$140.75	$140.75	$140.80
Purchase #7	$167.78	4.202%	$174.8301	$174.83	$174.85	$174.80
7 purchase totals =	$1,279.65		$1,388.6305	$1,388.62	$1,388.65	$1,388.60