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	$114.83	4.570%	$120.0777	$120.08	$120.10	$120.10
Purchase #2	$79.90	10.479%	$88.2727	$88.27	$88.25	$88.30
Purchase #3	$89.96	11.793%	$100.569	$100.57	$100.55	$100.60
Purchase #4	$64.81	4.448%	$67.6927	$67.69	$67.70	$67.70
Purchase #5	$82.97	11.711%	$92.6866	$92.69	$92.70	$92.70
Purchase #6	$116.45	12.410%	$130.9014	$130.90	$130.90	$130.90
Purchase #7	$89.48	5.687%	$94.5687	$94.57	$94.55	$94.60
7 purchase totals =	$638.40		$694.7688	$694.77	$694.75	$694.90