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	$37.98	11.802%	$42.4624	$42.46	$42.45	$42.50
Purchase #2	$9.48	6.732%	$10.1182	$10.12	$10.10	$10.10
Purchase #3	$72.64	12.857%	$81.9793	$81.98	$82.00	$82.00
Purchase #4	$44.36	11.504%	$49.4632	$49.46	$49.45	$49.50
Purchase #5	$236.63	3.231%	$244.2755	$244.28	$244.30	$244.30
Purchase #6	$86.34	3.312%	$89.1996	$89.20	$89.20	$89.20
Purchase #7	$240.36	12.405%	$270.1767	$270.18	$270.20	$270.20
7 purchase totals =	$727.79		$787.6749	$787.68	$787.70	$787.80