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	$39.90	7.128%	$42.7441	$42.74	$42.75	$42.70
Purchase #2	$56.41	6.272%	$59.948	$59.95	$59.95	$59.90
Purchase #3	$182.77	8.791%	$198.8373	$198.84	$198.85	$198.80
Purchase #4	$176.92	7.642%	$190.4402	$190.44	$190.45	$190.40
Purchase #5	$77.59	3.316%	$80.1629	$80.16	$80.15	$80.20
Purchase #6	$111.51	11.684%	$124.5388	$124.54	$124.55	$124.50
Purchase #7	$169.48	10.160%	$186.6992	$186.70	$186.70	$186.70
7 purchase totals =	$814.58		$883.3705	$883.37	$883.40	$883.20