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	$78.46	12.325%	$88.1302	$88.13	$88.15	$88.10
Purchase #2	$215.37	5.690%	$227.6246	$227.62	$227.60	$227.60
Purchase #3	$110.93	6.304%	$117.923	$117.92	$117.90	$117.90
Purchase #4	$152.49	6.835%	$162.9127	$162.91	$162.90	$162.90
Purchase #5	$96.45	4.313%	$100.6099	$100.61	$100.60	$100.60
Purchase #6	$78.37	11.545%	$87.4178	$87.42	$87.40	$87.40
Purchase #7	$215.48	10.186%	$237.4288	$237.43	$237.45	$237.40
7 purchase totals =	$947.55		$1,022.0470	$1,022.04	$1,022.00	$1,021.90