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	$94.95	5.836%	$100.4913	$100.49	$100.50	$100.50
Purchase #2	$159.86	5.333%	$168.3853	$168.39	$168.40	$168.40
Purchase #3	$27.30	10.412%	$30.1425	$30.14	$30.15	$30.10
Purchase #4	$78.80	12.254%	$88.4562	$88.46	$88.45	$88.50
Purchase #5	$69.72	10.519%	$77.0538	$77.05	$77.05	$77.10
Purchase #6	$55.45	5.517%	$58.5092	$58.51	$58.50	$58.50
Purchase #7	$27.46	6.804%	$29.3284	$29.33	$29.35	$29.30
7 purchase totals =	$513.54		$552.3667	$552.37	$552.40	$552.40