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	$112.27	6.132%	$119.1544	$119.15	$119.15	$119.20
Purchase #2	$90.36	10.330%	$99.6942	$99.69	$99.70	$99.70
Purchase #3	$116.84	12.130%	$131.0127	$131.01	$131.00	$131.00
Purchase #4	$148.88	5.151%	$156.5488	$156.55	$156.55	$156.50
Purchase #5	$190.47	4.685%	$199.3935	$199.39	$199.40	$199.40
Purchase #6	$28.85	11.546%	$32.181	$32.18	$32.20	$32.20
Purchase #7	$94.73	7.838%	$102.1549	$102.15	$102.15	$102.20
7 purchase totals =	$782.40		$840.1395	$840.12	$840.15	$840.20