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	$79.40	8.713%	$86.3181	$86.32	$86.30	$86.30
Purchase #2	$39.68	4.516%	$41.4719	$41.47	$41.45	$41.50
Purchase #3	$212.43	4.392%	$221.7599	$221.76	$221.75	$221.80
Purchase #4	$65.28	6.681%	$69.6414	$69.64	$69.65	$69.60
Purchase #5	$179.92	9.250%	$196.5626	$196.56	$196.55	$196.60
Purchase #6	$174.80	10.104%	$192.4618	$192.46	$192.45	$192.50
Purchase #7	$88.70	4.394%	$92.5975	$92.60	$92.60	$92.60
7 purchase totals =	$840.21		$900.8132	$900.81	$900.75	$900.90