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	$152.37	10.344%	$168.1312	$168.13	$168.15	$168.10
Purchase #2	$182.35	3.315%	$188.3949	$188.39	$188.40	$188.40
Purchase #3	$88.97	4.304%	$92.7993	$92.80	$92.80	$92.80
Purchase #4	$165.83	3.176%	$171.0968	$171.10	$171.10	$171.10
Purchase #5	$140.55	6.116%	$149.146	$149.15	$149.15	$149.10
Purchase #6	$112.98	9.685%	$123.9221	$123.92	$123.90	$123.90
Purchase #7	$55.44	13.238%	$62.7791	$62.78	$62.80	$62.80
7 purchase totals =	$898.49		$956.2694	$956.27	$956.30	$956.20