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	$92.59	8.139%	$100.1259	$100.13	$100.15	$100.10
Purchase #2	$172.80	13.132%	$195.4921	$195.49	$195.50	$195.50
Purchase #3	$101.40	4.108%	$105.5655	$105.57	$105.55	$105.60
Purchase #4	$227.66	5.199%	$239.496	$239.50	$239.50	$239.50
Purchase #5	$47.75	6.670%	$50.9349	$50.93	$50.95	$50.90
Purchase #6	$30.74	9.162%	$33.5564	$33.56	$33.55	$33.60
Purchase #7	$72.36	8.806%	$78.732	$78.73	$78.75	$78.70
7 purchase totals =	$745.30		$803.9028	$803.91	$803.95	$803.90