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	$34.55	12.728%	$38.9475	$38.95	$38.95	$38.90
Purchase #2	$92.47	8.803%	$100.6101	$100.61	$100.60	$100.60
Purchase #3	$34.33	9.481%	$37.5848	$37.58	$37.60	$37.60
Purchase #4	$211.78	5.637%	$223.718	$223.72	$223.70	$223.70
Purchase #5	$219.44	13.440%	$248.9327	$248.93	$248.95	$248.90
Purchase #6	$78.91	13.843%	$89.8335	$89.83	$89.85	$89.80
Purchase #7	$50.40	3.529%	$52.1786	$52.18	$52.20	$52.20
7 purchase totals =	$721.88		$791.8052	$791.80	$791.85	$791.70