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	$121.76	8.284%	$131.8466	$131.85	$131.85	$131.80
Purchase #2	$203.29	4.663%	$212.7694	$212.77	$212.75	$212.80
Purchase #3	$151.75	13.871%	$172.7992	$172.80	$172.80	$172.80
Purchase #4	$59.25	10.851%	$65.6792	$65.68	$65.70	$65.70
Purchase #5	$83.74	6.361%	$89.0667	$89.07	$89.05	$89.10
Purchase #6	$178.76	10.687%	$197.8641	$197.86	$197.85	$197.90
Purchase #7	$20.34	9.787%	$22.3307	$22.33	$22.35	$22.30
7 purchase totals =	$818.89		$892.3559	$892.36	$892.35	$892.40