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	$156.63	3.586%	$162.2468	$162.25	$162.25	$162.20
Purchase #2	$63.99	10.838%	$70.9252	$70.93	$70.95	$70.90
Purchase #3	$86.41	3.351%	$89.3056	$89.31	$89.30	$89.30
Purchase #4	$210.25	5.834%	$222.516	$222.52	$222.50	$222.50
Purchase #5	$215.76	11.458%	$240.4818	$240.48	$240.50	$240.50
Purchase #6	$25.41	9.860%	$27.9154	$27.92	$27.90	$27.90
Purchase #7	$7.87	5.291%	$8.2864	$8.29	$8.30	$8.30
7 purchase totals =	$766.32		$821.6772	$821.70	$821.70	$821.60