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	$60.39	13.413%	$68.4901	$68.49	$68.50	$68.50
Purchase #2	$204.97	8.447%	$222.2838	$222.28	$222.30	$222.30
Purchase #3	$227.40	12.727%	$256.3412	$256.34	$256.35	$256.30
Purchase #4	$139.27	9.308%	$152.2333	$152.23	$152.25	$152.20
Purchase #5	$112.90	3.727%	$117.1078	$117.11	$117.10	$117.10
Purchase #6	$31.88	5.145%	$33.5202	$33.52	$33.50	$33.50
Purchase #7	$106.63	12.425%	$119.8788	$119.88	$119.90	$119.90
7 purchase totals =	$883.44		$969.8552	$969.85	$969.90	$969.80