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	$67.77	8.274%	$73.3773	$73.38	$73.40	$73.40
Purchase #2	$228.70	3.393%	$236.4598	$236.46	$236.45	$236.50
Purchase #3	$106.51	3.140%	$109.8544	$109.85	$109.85	$109.90
Purchase #4	$84.43	11.665%	$94.2788	$94.28	$94.30	$94.30
Purchase #5	$79.33	3.731%	$82.2898	$82.29	$82.30	$82.30
Purchase #6	$130.25	7.728%	$140.3157	$140.32	$140.30	$140.30
Purchase #7	$44.97	13.723%	$51.1412	$51.14	$51.15	$51.10
7 purchase totals =	$741.96		$787.7170	$787.72	$787.75	$787.80