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	$25.47	11.712%	$28.453	$28.45	$28.45	$28.50
Purchase #2	$83.46	3.436%	$86.3277	$86.33	$86.35	$86.30
Purchase #3	$219.70	6.106%	$233.1149	$233.11	$233.10	$233.10
Purchase #4	$232.47	4.576%	$243.1078	$243.11	$243.10	$243.10
Purchase #5	$68.64	11.791%	$76.7333	$76.73	$76.75	$76.70
Purchase #6	$205.45	11.254%	$228.5713	$228.57	$228.55	$228.60
Purchase #7	$95.41	10.648%	$105.5693	$105.57	$105.55	$105.60
7 purchase totals =	$930.60		$1,001.8773	$1,001.87	$1,001.85	$1,001.90