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	$148.89	6.353%	$158.349	$158.35	$158.35	$158.30
Purchase #2	$132.48	13.156%	$149.9091	$149.91	$149.90	$149.90
Purchase #3	$229.26	11.436%	$255.4782	$255.48	$255.50	$255.50
Purchase #4	$48.86	13.421%	$55.4175	$55.42	$55.40	$55.40
Purchase #5	$174.88	11.832%	$195.5718	$195.57	$195.55	$195.60
Purchase #6	$144.88	13.866%	$164.9691	$164.97	$164.95	$165.00
Purchase #7	$100.53	12.643%	$113.24	$113.24	$113.25	$113.20
7 purchase totals =	$979.78		$1,092.9347	$1,092.94	$1,092.90	$1,092.90