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	$144.48	5.794%	$152.8512	$152.85	$152.85	$152.90
Purchase #2	$133.61	10.797%	$148.0359	$148.04	$148.05	$148.00
Purchase #3	$88.66	9.321%	$96.924	$96.92	$96.90	$96.90
Purchase #4	$90.55	5.281%	$95.3319	$95.33	$95.35	$95.30
Purchase #5	$194.38	13.253%	$220.1412	$220.14	$220.15	$220.10
Purchase #6	$26.38	9.873%	$28.9845	$28.98	$29.00	$29.00
Purchase #7	$72.57	8.392%	$78.6601	$78.66	$78.65	$78.70
7 purchase totals =	$750.63		$820.9288	$820.92	$820.95	$820.90