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	$148.28	13.467%	$168.2489	$168.25	$168.25	$168.20
Purchase #2	$26.25	4.411%	$27.4079	$27.41	$27.40	$27.40
Purchase #3	$25.88	13.192%	$29.2941	$29.29	$29.30	$29.30
Purchase #4	$196.55	7.335%	$210.9669	$210.97	$210.95	$211.00
Purchase #5	$72.41	13.488%	$82.1767	$82.18	$82.20	$82.20
Purchase #6	$130.72	6.319%	$138.9802	$138.98	$139.00	$139.00
Purchase #7	$99.61	9.732%	$109.304	$109.30	$109.30	$109.30
7 purchase totals =	$699.70		$766.3787	$766.38	$766.40	$766.40