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	$133.61	13.123%	$151.1436	$151.14	$151.15	$151.10
Purchase #2	$63.25	4.133%	$65.8641	$65.86	$65.85	$65.90
Purchase #3	$115.58	8.410%	$125.3003	$125.30	$125.30	$125.30
Purchase #4	$73.53	13.194%	$83.2315	$83.23	$83.25	$83.20
Purchase #5	$138.91	9.646%	$152.3093	$152.31	$152.30	$152.30
Purchase #6	$161.33	10.497%	$178.2648	$178.26	$178.25	$178.30
Purchase #7	$28.28	10.393%	$31.2191	$31.22	$31.20	$31.20
7 purchase totals =	$714.49		$787.3327	$787.32	$787.30	$787.30