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	$186.48	3.432%	$192.88	$192.88	$192.90	$192.90
Purchase #2	$91.66	8.284%	$99.2531	$99.25	$99.25	$99.30
Purchase #3	$135.57	5.753%	$143.3693	$143.37	$143.35	$143.40
Purchase #4	$234.75	9.594%	$257.2719	$257.27	$257.25	$257.30
Purchase #5	$20.35	9.218%	$22.2259	$22.23	$22.25	$22.20
Purchase #6	$167.83	9.518%	$183.8041	$183.80	$183.80	$183.80
Purchase #7	$89.46	12.586%	$100.7194	$100.72	$100.70	$100.70
7 purchase totals =	$926.10		$999.5237	$999.52	$999.50	$999.60