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	$91.81	11.218%	$102.1092	$102.11	$102.10	$102.10
Purchase #2	$67.90	5.782%	$71.826	$71.83	$71.85	$71.80
Purchase #3	$188.35	9.404%	$206.0624	$206.06	$206.05	$206.10
Purchase #4	$9.86	8.145%	$10.6631	$10.66	$10.65	$10.70
Purchase #5	$231.34	10.538%	$255.7186	$255.72	$255.70	$255.70
Purchase #6	$35.85	4.672%	$37.5249	$37.52	$37.50	$37.50
Purchase #7	$242.30	9.693%	$265.7861	$265.79	$265.80	$265.80
7 purchase totals =	$867.41		$949.6903	$949.69	$949.65	$949.70