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	$60.25	9.851%	$66.1852	$66.19	$66.20	$66.20
Purchase #2	$43.81	6.753%	$46.7685	$46.77	$46.75	$46.80
Purchase #3	$33.37	11.785%	$37.3027	$37.30	$37.30	$37.30
Purchase #4	$73.30	6.870%	$78.3357	$78.34	$78.35	$78.30
Purchase #5	$179.30	10.182%	$197.5563	$197.56	$197.55	$197.60
Purchase #6	$139.79	11.514%	$155.8854	$155.89	$155.90	$155.90
Purchase #7	$233.36	7.729%	$251.3964	$251.40	$251.40	$251.40
7 purchase totals =	$763.18		$833.4302	$833.45	$833.45	$833.50