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	$125.75	11.514%	$140.2289	$140.23	$140.25	$140.20
Purchase #2	$176.67	5.284%	$186.0052	$186.01	$186.00	$186.00
Purchase #3	$111.54	6.194%	$118.4488	$118.45	$118.45	$118.40
Purchase #4	$25.62	8.596%	$27.8223	$27.82	$27.80	$27.80
Purchase #5	$78.74	5.199%	$82.8337	$82.83	$82.85	$82.80
Purchase #6	$98.66	9.118%	$107.6558	$107.66	$107.65	$107.70
Purchase #7	$82.74	3.298%	$85.4688	$85.47	$85.45	$85.50
7 purchase totals =	$699.72		$748.4635	$748.47	$748.45	$748.40