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	$101.50	13.703%	$115.4085	$115.41	$115.40	$115.40
Purchase #2	$21.66	5.404%	$22.8305	$22.83	$22.85	$22.80
Purchase #3	$59.45	10.145%	$65.4812	$65.48	$65.50	$65.50
Purchase #4	$97.44	13.478%	$110.573	$110.57	$110.55	$110.60
Purchase #5	$82.99	9.435%	$90.8201	$90.82	$90.80	$90.80
Purchase #6	$177.66	5.516%	$187.4597	$187.46	$187.45	$187.50
Purchase #7	$59.88	12.809%	$67.55	$67.55	$67.55	$67.60
7 purchase totals =	$600.58		$660.1230	$660.12	$660.10	$660.20