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	$49.93	10.106%	$54.9759	$54.98	$55.00	$55.00
Purchase #2	$118.68	11.292%	$132.0813	$132.08	$132.10	$132.10
Purchase #3	$119.33	10.146%	$131.4372	$131.44	$131.45	$131.40
Purchase #4	$40.38	5.359%	$42.544	$42.54	$42.55	$42.50
Purchase #5	$77.53	9.765%	$85.1008	$85.10	$85.10	$85.10
Purchase #6	$60.67	3.432%	$62.7522	$62.75	$62.75	$62.80
Purchase #7	$6.45	10.742%	$7.1429	$7.14	$7.15	$7.10
7 purchase totals =	$472.97		$516.0343	$516.03	$516.10	$516.00