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	$198.34	10.234%	$218.6381	$218.64	$218.65	$218.60
Purchase #2	$87.55	13.114%	$99.0313	$99.03	$99.05	$99.00
Purchase #3	$87.48	3.135%	$90.2225	$90.22	$90.20	$90.20
Purchase #4	$250.34	5.601%	$264.3615	$264.36	$264.35	$264.40
Purchase #5	$44.77	11.436%	$49.8899	$49.89	$49.90	$49.90
Purchase #6	$45.57	8.146%	$49.2821	$49.28	$49.30	$49.30
Purchase #7	$196.67	9.478%	$215.3104	$215.31	$215.30	$215.30
7 purchase totals =	$910.72		$986.7358	$986.73	$986.75	$986.70