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	$48.56	13.713%	$55.219	$55.22	$55.20	$55.20
Purchase #2	$236.27	10.429%	$260.9106	$260.91	$260.90	$260.90
Purchase #3	$60.72	13.300%	$68.7958	$68.80	$68.80	$68.80
Purchase #4	$168.73	6.436%	$179.5895	$179.59	$179.60	$179.60
Purchase #5	$104.27	9.154%	$113.8149	$113.81	$113.80	$113.80
Purchase #6	$199.58	3.506%	$206.5773	$206.58	$206.60	$206.60
Purchase #7	$159.50	3.774%	$165.5195	$165.52	$165.50	$165.50
7 purchase totals =	$977.63		$1,050.4266	$1,050.43	$1,050.40	$1,050.40