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	$51.75	6.689%	$55.2116	$55.21	$55.20	$55.20
Purchase #2	$139.99	3.392%	$144.7385	$144.74	$144.75	$144.70
Purchase #3	$114.31	12.490%	$128.5873	$128.59	$128.60	$128.60
Purchase #4	$169.77	9.292%	$185.545	$185.55	$185.55	$185.50
Purchase #5	$227.96	11.758%	$254.7635	$254.76	$254.75	$254.80
Purchase #6	$152.44	9.226%	$166.5041	$166.50	$166.50	$166.50
Purchase #7	$123.38	11.303%	$137.3256	$137.33	$137.35	$137.30
7 purchase totals =	$979.60		$1,072.6756	$1,072.68	$1,072.70	$1,072.60