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	$39.70	8.615%	$43.1202	$43.12	$43.10	$43.10
Purchase #2	$192.48	6.138%	$204.2944	$204.29	$204.30	$204.30
Purchase #3	$169.62	9.309%	$185.4099	$185.41	$185.40	$185.40
Purchase #4	$17.55	5.604%	$18.5335	$18.53	$18.55	$18.50
Purchase #5	$153.70	8.672%	$167.0289	$167.03	$167.05	$167.00
Purchase #6	$53.34	12.145%	$59.8181	$59.82	$59.80	$59.80
Purchase #7	$164.98	8.285%	$178.6486	$178.65	$178.65	$178.60
7 purchase totals =	$791.37		$856.8536	$856.85	$856.85	$856.70