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	$227.32	10.287%	$250.7044	$250.70	$250.70	$250.70
Purchase #2	$88.94	12.835%	$100.3554	$100.36	$100.35	$100.40
Purchase #3	$227.33	3.611%	$235.5389	$235.54	$235.55	$235.50
Purchase #4	$37.84	5.356%	$39.8667	$39.87	$39.85	$39.90
Purchase #5	$53.57	10.598%	$59.2473	$59.25	$59.25	$59.20
Purchase #6	$89.53	10.213%	$98.6737	$98.67	$98.65	$98.70
Purchase #7	$184.40	12.834%	$208.0659	$208.07	$208.05	$208.10
7 purchase totals =	$908.93		$992.4523	$992.46	$992.40	$992.50