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	$98.52	12.140%	$110.4803	$110.48	$110.50	$110.50
Purchase #2	$62.68	7.708%	$67.5114	$67.51	$67.50	$67.50
Purchase #3	$224.53	4.458%	$234.5395	$234.54	$234.55	$234.50
Purchase #4	$33.45	13.260%	$37.8855	$37.89	$37.90	$37.90
Purchase #5	$54.57	13.256%	$61.8038	$61.80	$61.80	$61.80
Purchase #6	$242.50	11.751%	$270.9962	$271.00	$271.00	$271.00
Purchase #7	$63.33	5.371%	$66.7315	$66.73	$66.75	$66.70
7 purchase totals =	$779.58		$849.9482	$849.95	$850.00	$849.90