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	$229.63	3.486%	$237.6349	$237.63	$237.65	$237.60
Purchase #2	$247.25	11.745%	$276.2895	$276.29	$276.30	$276.30
Purchase #3	$93.55	4.240%	$97.5165	$97.52	$97.50	$97.50
Purchase #4	$189.63	9.132%	$206.947	$206.95	$206.95	$206.90
Purchase #5	$38.53	5.288%	$40.5675	$40.57	$40.55	$40.60
Purchase #6	$221.53	7.718%	$238.6277	$238.63	$238.65	$238.60
Purchase #7	$79.89	12.481%	$89.8611	$89.86	$89.85	$89.90
7 purchase totals =	$1,100.01		$1,187.4442	$1,187.45	$1,187.45	$1,187.40