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	$194.65	8.654%	$211.495	$211.50	$211.50	$211.50
Purchase #2	$141.88	3.473%	$146.8075	$146.81	$146.80	$146.80
Purchase #3	$38.66	9.282%	$42.2484	$42.25	$42.25	$42.20
Purchase #4	$194.91	11.141%	$216.6249	$216.62	$216.60	$216.60
Purchase #5	$92.83	13.440%	$105.3064	$105.31	$105.30	$105.30
Purchase #6	$235.47	6.276%	$250.2481	$250.25	$250.25	$250.20
Purchase #7	$20.40	7.331%	$21.8955	$21.90	$21.90	$21.90
7 purchase totals =	$918.80		$994.6258	$994.64	$994.60	$994.50