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	$68.68	9.851%	$75.4457	$75.45	$75.45	$75.40
Purchase #2	$30.66	7.659%	$33.0082	$33.01	$33.00	$33.00
Purchase #3	$179.56	6.431%	$191.1075	$191.11	$191.10	$191.10
Purchase #4	$100.33	3.549%	$103.8907	$103.89	$103.90	$103.90
Purchase #5	$224.50	12.839%	$253.3236	$253.32	$253.30	$253.30
Purchase #6	$71.55	10.523%	$79.0792	$79.08	$79.10	$79.10
Purchase #7	$50.54	10.302%	$55.7466	$55.75	$55.75	$55.70
7 purchase totals =	$725.82		$791.6015	$791.61	$791.60	$791.50