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	$95.29	3.787%	$98.8986	$98.90	$98.90	$98.90
Purchase #2	$189.69	5.108%	$199.3794	$199.38	$199.40	$199.40
Purchase #3	$130.80	9.190%	$142.8205	$142.82	$142.80	$142.80
Purchase #4	$208.30	7.364%	$223.6392	$223.64	$223.65	$223.60
Purchase #5	$98.28	13.654%	$111.6992	$111.70	$111.70	$111.70
Purchase #6	$101.66	6.607%	$108.3767	$108.38	$108.40	$108.40
Purchase #7	$25.97	5.606%	$27.4259	$27.43	$27.45	$27.40
7 purchase totals =	$849.99		$912.2395	$912.25	$912.30	$912.20