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	$16.96	3.374%	$17.5322	$17.53	$17.55	$17.50
Purchase #2	$136.56	11.536%	$152.3136	$152.31	$152.30	$152.30
Purchase #3	$222.91	12.191%	$250.085	$250.09	$250.10	$250.10
Purchase #4	$115.99	6.322%	$123.3229	$123.32	$123.30	$123.30
Purchase #5	$177.64	5.147%	$186.7831	$186.78	$186.80	$186.80
Purchase #6	$221.88	11.645%	$247.7179	$247.72	$247.70	$247.70
Purchase #7	$24.33	5.754%	$25.7299	$25.73	$25.75	$25.70
7 purchase totals =	$916.27		$1,003.4846	$1,003.48	$1,003.50	$1,003.40