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	$84.64	6.223%	$89.9071	$89.91	$89.90	$89.90
Purchase #2	$31.81	12.338%	$35.7347	$35.73	$35.75	$35.70
Purchase #3	$16.72	11.783%	$18.6901	$18.69	$18.70	$18.70
Purchase #4	$247.85	4.199%	$258.2572	$258.26	$258.25	$258.30
Purchase #5	$64.63	12.462%	$72.6842	$72.68	$72.70	$72.70
Purchase #6	$102.81	5.102%	$108.0554	$108.06	$108.05	$108.10
Purchase #7	$123.31	11.371%	$137.3316	$137.33	$137.35	$137.30
7 purchase totals =	$671.77		$720.6603	$720.66	$720.70	$720.70