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	$90.31	6.489%	$96.1702	$96.17	$96.15	$96.20
Purchase #2	$209.25	8.310%	$226.6387	$226.64	$226.65	$226.60
Purchase #3	$118.79	4.309%	$123.9087	$123.91	$123.90	$123.90
Purchase #4	$107.59	8.334%	$116.5566	$116.56	$116.55	$116.60
Purchase #5	$96.71	13.255%	$109.5289	$109.53	$109.55	$109.50
Purchase #6	$236.35	11.808%	$264.2582	$264.26	$264.25	$264.30
Purchase #7	$67.37	4.614%	$70.4785	$70.48	$70.50	$70.50
7 purchase totals =	$926.37		$1,007.5398	$1,007.55	$1,007.55	$1,007.60