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	$6.70	6.390%	$7.1281	$7.13	$7.15	$7.10
Purchase #2	$84.56	7.410%	$90.8259	$90.83	$90.85	$90.80
Purchase #3	$36.25	5.237%	$38.1484	$38.15	$38.15	$38.10
Purchase #4	$106.65	8.514%	$115.7302	$115.73	$115.75	$115.70
Purchase #5	$42.85	8.592%	$46.5317	$46.53	$46.55	$46.50
Purchase #6	$222.80	5.599%	$235.2746	$235.27	$235.25	$235.30
Purchase #7	$229.70	9.136%	$250.6854	$250.69	$250.70	$250.70
7 purchase totals =	$729.51		$784.3243	$784.33	$784.40	$784.20