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	$146.35	5.856%	$154.9203	$154.92	$154.90	$154.90
Purchase #2	$64.40	12.219%	$72.269	$72.27	$72.25	$72.30
Purchase #3	$58.32	8.592%	$63.3309	$63.33	$63.35	$63.30
Purchase #4	$112.60	7.312%	$120.8333	$120.83	$120.85	$120.80
Purchase #5	$13.54	10.333%	$14.9391	$14.94	$14.95	$14.90
Purchase #6	$79.77	9.760%	$87.5556	$87.56	$87.55	$87.60
Purchase #7	$128.75	13.740%	$146.4403	$146.44	$146.45	$146.40
7 purchase totals =	$603.73		$660.2885	$660.29	$660.30	$660.20