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	$132.89	12.427%	$149.4042	$149.40	$149.40	$149.40
Purchase #2	$79.91	12.430%	$89.8428	$89.84	$89.85	$89.80
Purchase #3	$47.36	6.759%	$50.5611	$50.56	$50.55	$50.60
Purchase #4	$211.77	11.793%	$236.744	$236.74	$236.75	$236.70
Purchase #5	$40.53	11.705%	$45.274	$45.27	$45.25	$45.30
Purchase #6	$134.89	11.347%	$150.196	$150.20	$150.20	$150.20
Purchase #7	$85.75	7.414%	$92.1075	$92.11	$92.10	$92.10
7 purchase totals =	$733.10		$814.1296	$814.12	$814.10	$814.10