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	$147.82	12.338%	$166.058	$166.06	$166.05	$166.10
Purchase #2	$110.42	11.800%	$123.4496	$123.45	$123.45	$123.40
Purchase #3	$175.48	10.633%	$194.1388	$194.14	$194.15	$194.10
Purchase #4	$141.66	7.651%	$152.4984	$152.50	$152.50	$152.50
Purchase #5	$132.79	6.842%	$141.8755	$141.88	$141.90	$141.90
Purchase #6	$159.94	6.275%	$169.9762	$169.98	$170.00	$170.00
Purchase #7	$38.36	10.304%	$42.3126	$42.31	$42.30	$42.30
7 purchase totals =	$906.47		$990.3091	$990.32	$990.35	$990.30