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	$225.48	5.715%	$238.3662	$238.37	$238.35	$238.40
Purchase #2	$36.92	4.403%	$38.5456	$38.55	$38.55	$38.50
Purchase #3	$247.31	9.705%	$271.3114	$271.31	$271.30	$271.30
Purchase #4	$76.69	7.154%	$82.1764	$82.18	$82.20	$82.20
Purchase #5	$26.74	10.644%	$29.5862	$29.59	$29.60	$29.60
Purchase #6	$109.75	9.820%	$120.5275	$120.53	$120.55	$120.50
Purchase #7	$172.44	7.742%	$185.7903	$185.79	$185.80	$185.80
7 purchase totals =	$895.33		$966.3036	$966.32	$966.35	$966.30