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	$24.52	10.607%	$27.1208	$27.12	$27.10	$27.10
Purchase #2	$41.31	5.106%	$43.4193	$43.42	$43.40	$43.40
Purchase #3	$152.44	12.361%	$171.2831	$171.28	$171.30	$171.30
Purchase #4	$30.77	7.184%	$32.9805	$32.98	$33.00	$33.00
Purchase #5	$105.59	11.640%	$117.8807	$117.88	$117.90	$117.90
Purchase #6	$58.94	4.380%	$61.5216	$61.52	$61.50	$61.50
Purchase #7	$170.77	11.820%	$190.955	$190.96	$190.95	$191.00
7 purchase totals =	$584.34		$645.1610	$645.16	$645.15	$645.20