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	$74.73	3.735%	$77.5212	$77.52	$77.50	$77.50
Purchase #2	$112.40	12.449%	$126.3927	$126.39	$126.40	$126.40
Purchase #3	$38.86	7.725%	$41.8619	$41.86	$41.85	$41.90
Purchase #4	$204.64	11.368%	$227.9035	$227.90	$227.90	$227.90
Purchase #5	$35.86	12.654%	$40.3977	$40.40	$40.40	$40.40
Purchase #6	$185.40	7.289%	$198.9138	$198.91	$198.90	$198.90
Purchase #7	$238.90	12.164%	$267.9598	$267.96	$267.95	$268.00
7 purchase totals =	$890.79		$980.9506	$980.94	$980.90	$981.00