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	$99.82	5.404%	$105.2143	$105.21	$105.20	$105.20
Purchase #2	$18.72	9.240%	$20.4497	$20.45	$20.45	$20.40
Purchase #3	$190.53	8.355%	$206.4488	$206.45	$206.45	$206.40
Purchase #4	$57.39	4.705%	$60.0902	$60.09	$60.10	$60.10
Purchase #5	$123.86	11.696%	$138.3467	$138.35	$138.35	$138.30
Purchase #6	$99.58	11.561%	$111.0924	$111.09	$111.10	$111.10
Purchase #7	$28.69	11.187%	$31.8996	$31.90	$31.90	$31.90
7 purchase totals =	$618.59		$673.5417	$673.54	$673.55	$673.40