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	$82.92	7.674%	$89.2833	$89.28	$89.30	$89.30
Purchase #2	$152.75	7.852%	$164.7439	$164.74	$164.75	$164.70
Purchase #3	$212.43	3.496%	$219.8566	$219.86	$219.85	$219.90
Purchase #4	$246.99	3.570%	$255.8075	$255.81	$255.80	$255.80
Purchase #5	$104.27	8.285%	$112.9088	$112.91	$112.90	$112.90
Purchase #6	$236.73	5.560%	$249.8922	$249.89	$249.90	$249.90
Purchase #7	$156.46	11.540%	$174.5155	$174.52	$174.50	$174.50
7 purchase totals =	$1,192.55		$1,267.0078	$1,267.01	$1,267.00	$1,267.00