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	$158.60	10.278%	$174.9009	$174.90	$174.90	$174.90
Purchase #2	$123.76	6.220%	$131.4579	$131.46	$131.45	$131.50
Purchase #3	$144.79	3.288%	$149.5507	$149.55	$149.55	$149.60
Purchase #4	$56.93	4.383%	$59.4252	$59.43	$59.45	$59.40
Purchase #5	$69.81	4.347%	$72.8446	$72.84	$72.85	$72.80
Purchase #6	$195.53	6.753%	$208.7341	$208.73	$208.75	$208.70
Purchase #7	$179.34	9.827%	$196.9637	$196.96	$196.95	$197.00
7 purchase totals =	$928.76		$993.8771	$993.87	$993.90	$993.90