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	$20.42	4.116%	$21.2605	$21.26	$21.25	$21.30
Purchase #2	$162.39	7.570%	$174.6829	$174.68	$174.70	$174.70
Purchase #3	$81.69	13.663%	$92.8513	$92.85	$92.85	$92.90
Purchase #4	$140.60	3.234%	$145.147	$145.15	$145.15	$145.10
Purchase #5	$142.50	5.514%	$150.3575	$150.36	$150.35	$150.40
Purchase #6	$6.63	13.419%	$7.5197	$7.52	$7.50	$7.50
Purchase #7	$73.49	7.385%	$78.9172	$78.92	$78.90	$78.90
7 purchase totals =	$627.72		$670.7361	$670.74	$670.70	$670.80