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	$154.38	9.297%	$168.7327	$168.73	$168.75	$168.70
Purchase #2	$104.61	12.628%	$117.8202	$117.82	$117.80	$117.80
Purchase #3	$122.29	12.435%	$137.4968	$137.50	$137.50	$137.50
Purchase #4	$55.57	7.265%	$59.6072	$59.61	$59.60	$59.60
Purchase #5	$134.31	9.303%	$146.8049	$146.80	$146.80	$146.80
Purchase #6	$46.46	5.757%	$49.1347	$49.13	$49.15	$49.10
Purchase #7	$105.60	7.270%	$113.2771	$113.28	$113.30	$113.30
7 purchase totals =	$723.22		$792.8736	$792.87	$792.90	$792.80