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	$67.94	5.260%	$71.5136	$71.51	$71.50	$71.50
Purchase #2	$218.57	3.480%	$226.1762	$226.18	$226.20	$226.20
Purchase #3	$224.64	11.606%	$250.7117	$250.71	$250.70	$250.70
Purchase #4	$124.83	11.434%	$139.1031	$139.10	$139.10	$139.10
Purchase #5	$79.79	4.583%	$83.4468	$83.45	$83.45	$83.40
Purchase #6	$80.63	7.395%	$86.5926	$86.59	$86.60	$86.60
Purchase #7	$29.75	11.282%	$33.1064	$33.11	$33.10	$33.10
7 purchase totals =	$826.15		$890.6504	$890.65	$890.65	$890.60