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	$51.96	10.451%	$57.3903	$57.39	$57.40	$57.40
Purchase #2	$193.89	10.753%	$214.739	$214.74	$214.75	$214.70
Purchase #3	$218.43	11.409%	$243.3507	$243.35	$243.35	$243.40
Purchase #4	$7.50	12.852%	$8.4639	$8.46	$8.45	$8.50
Purchase #5	$88.72	12.440%	$99.7568	$99.76	$99.75	$99.80
Purchase #6	$76.59	11.736%	$85.5786	$85.58	$85.60	$85.60
Purchase #7	$172.33	12.871%	$194.5106	$194.51	$194.50	$194.50
7 purchase totals =	$809.42		$903.7899	$903.79	$903.80	$903.90