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	$35.64	13.673%	$40.5131	$40.51	$40.50	$40.50
Purchase #2	$19.42	4.802%	$20.3525	$20.35	$20.35	$20.40
Purchase #3	$143.73	10.555%	$158.9007	$158.90	$158.90	$158.90
Purchase #4	$56.33	11.241%	$62.6621	$62.66	$62.65	$62.70
Purchase #5	$189.98	4.518%	$198.5633	$198.56	$198.55	$198.60
Purchase #6	$91.65	13.316%	$103.8541	$103.85	$103.85	$103.90
Purchase #7	$105.95	3.867%	$110.0471	$110.05	$110.05	$110.00
7 purchase totals =	$642.70		$694.8929	$694.88	$694.85	$695.00