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	$30.44	5.517%	$32.1194	$32.12	$32.10	$32.10
Purchase #2	$138.82	8.449%	$150.5489	$150.55	$150.55	$150.50
Purchase #3	$204.59	5.746%	$216.3457	$216.35	$216.35	$216.30
Purchase #4	$31.94	8.263%	$34.5792	$34.58	$34.60	$34.60
Purchase #5	$69.56	4.635%	$72.7841	$72.78	$72.80	$72.80
Purchase #6	$15.51	5.312%	$16.3339	$16.33	$16.35	$16.30
Purchase #7	$135.76	10.870%	$150.5171	$150.52	$150.50	$150.50
7 purchase totals =	$626.62		$673.2283	$673.23	$673.25	$673.10