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	$101.78	13.586%	$115.6078	$115.61	$115.60	$115.60
Purchase #2	$105.51	3.745%	$109.4613	$109.46	$109.45	$109.50
Purchase #3	$142.99	11.553%	$159.5096	$159.51	$159.50	$159.50
Purchase #4	$60.99	4.743%	$63.8828	$63.88	$63.90	$63.90
Purchase #5	$65.34	11.362%	$72.7639	$72.76	$72.75	$72.80
Purchase #6	$229.63	3.555%	$237.7933	$237.79	$237.80	$237.80
Purchase #7	$41.37	3.790%	$42.9379	$42.94	$42.95	$42.90
7 purchase totals =	$747.61		$801.9566	$801.95	$801.95	$802.00