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	$90.70	12.755%	$102.2688	$102.27	$102.25	$102.30
Purchase #2	$168.85	9.827%	$185.4429	$185.44	$185.45	$185.40
Purchase #3	$83.29	4.231%	$86.814	$86.81	$86.80	$86.80
Purchase #4	$106.86	9.736%	$117.2639	$117.26	$117.25	$117.30
Purchase #5	$64.59	8.122%	$69.836	$69.84	$69.85	$69.80
Purchase #6	$161.76	6.556%	$172.365	$172.37	$172.35	$172.40
Purchase #7	$96.79	9.107%	$105.6047	$105.60	$105.60	$105.60
7 purchase totals =	$772.84		$839.5953	$839.59	$839.55	$839.60