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	$163.98	4.594%	$171.5132	$171.51	$171.50	$171.50
Purchase #2	$126.39	10.394%	$139.527	$139.53	$139.55	$139.50
Purchase #3	$202.52	10.470%	$223.7238	$223.72	$223.70	$223.70
Purchase #4	$201.40	9.221%	$219.9711	$219.97	$219.95	$220.00
Purchase #5	$97.78	13.315%	$110.7994	$110.80	$110.80	$110.80
Purchase #6	$59.59	3.609%	$61.7406	$61.74	$61.75	$61.70
Purchase #7	$94.50	9.548%	$103.5229	$103.52	$103.50	$103.50
7 purchase totals =	$946.16		$1,030.7980	$1,030.79	$1,030.75	$1,030.70