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	$143.82	10.208%	$158.5011	$158.50	$158.50	$158.50
Purchase #2	$40.99	4.676%	$42.9067	$42.91	$42.90	$42.90
Purchase #3	$131.41	12.408%	$147.7154	$147.72	$147.70	$147.70
Purchase #4	$33.42	5.502%	$35.2588	$35.26	$35.25	$35.30
Purchase #5	$191.30	3.626%	$198.2365	$198.24	$198.25	$198.20
Purchase #6	$90.43	3.359%	$93.4675	$93.47	$93.45	$93.50
Purchase #7	$131.76	12.249%	$147.8993	$147.90	$147.90	$147.90
7 purchase totals =	$763.13		$823.9853	$824.00	$823.95	$824.00