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	$242.84	6.500%	$258.6246	$258.62	$258.60	$258.60
Purchase #2	$128.98	10.454%	$142.4636	$142.46	$142.45	$142.50
Purchase #3	$79.65	7.212%	$85.3944	$85.39	$85.40	$85.40
Purchase #4	$83.42	10.158%	$91.8938	$91.89	$91.90	$91.90
Purchase #5	$150.41	5.319%	$158.4103	$158.41	$158.40	$158.40
Purchase #6	$230.73	11.849%	$258.0692	$258.07	$258.05	$258.10
Purchase #7	$229.82	7.260%	$246.5049	$246.50	$246.50	$246.50
7 purchase totals =	$1,145.85		$1,241.3608	$1,241.34	$1,241.30	$1,241.40