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	$100.38	3.399%	$103.7919	$103.79	$103.80	$103.80
Purchase #2	$81.30	8.757%	$88.4194	$88.42	$88.40	$88.40
Purchase #3	$60.62	7.597%	$65.2253	$65.23	$65.25	$65.20
Purchase #4	$191.46	11.625%	$213.7172	$213.72	$213.70	$213.70
Purchase #5	$59.27	11.130%	$65.8668	$65.87	$65.85	$65.90
Purchase #6	$60.55	11.442%	$67.4781	$67.48	$67.50	$67.50
Purchase #7	$139.33	8.201%	$150.7565	$150.76	$150.75	$150.80
7 purchase totals =	$692.91		$755.2552	$755.27	$755.25	$755.30