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	$141.58	12.520%	$159.3058	$159.31	$159.30	$159.30
Purchase #2	$78.72	9.479%	$86.1819	$86.18	$86.20	$86.20
Purchase #3	$245.31	7.519%	$263.7549	$263.75	$263.75	$263.80
Purchase #4	$179.81	3.124%	$185.4273	$185.43	$185.45	$185.40
Purchase #5	$32.76	13.264%	$37.1053	$37.11	$37.10	$37.10
Purchase #6	$201.71	3.540%	$208.8505	$208.85	$208.85	$208.90
Purchase #7	$240.36	12.226%	$269.7464	$269.75	$269.75	$269.70
7 purchase totals =	$1,120.25		$1,210.3721	$1,210.38	$1,210.40	$1,210.40