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	$178.79	12.147%	$200.5076	$200.51	$200.50	$200.50
Purchase #2	$115.97	4.780%	$121.5134	$121.51	$121.50	$121.50
Purchase #3	$65.69	10.597%	$72.6512	$72.65	$72.65	$72.70
Purchase #4	$237.56	11.487%	$264.8485	$264.85	$264.85	$264.80
Purchase #5	$223.82	4.331%	$233.5136	$233.51	$233.50	$233.50
Purchase #6	$226.80	11.839%	$253.6509	$253.65	$253.65	$253.70
Purchase #7	$73.97	4.688%	$77.4377	$77.44	$77.45	$77.40
7 purchase totals =	$1,122.60		$1,224.1229	$1,224.12	$1,224.10	$1,224.10