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	$216.75	12.157%	$243.1003	$243.10	$243.10	$243.10
Purchase #2	$91.81	8.345%	$99.4715	$99.47	$99.45	$99.50
Purchase #3	$186.35	12.261%	$209.1984	$209.20	$209.20	$209.20
Purchase #4	$49.81	10.745%	$55.1621	$55.16	$55.15	$55.20
Purchase #5	$7.90	12.134%	$8.8586	$8.86	$8.85	$8.90
Purchase #6	$246.88	12.821%	$278.5325	$278.53	$278.55	$278.50
Purchase #7	$106.67	4.799%	$111.7891	$111.79	$111.80	$111.80
7 purchase totals =	$906.17		$1,006.1125	$1,006.11	$1,006.10	$1,006.20