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	$226.42	11.726%	$252.97	$252.97	$252.95	$253.00
Purchase #2	$175.64	5.437%	$185.1895	$185.19	$185.20	$185.20
Purchase #3	$51.52	3.711%	$53.4319	$53.43	$53.45	$53.40
Purchase #4	$28.48	12.531%	$32.0488	$32.05	$32.05	$32.00
Purchase #5	$222.59	9.345%	$243.391	$243.39	$243.40	$243.40
Purchase #6	$83.37	10.328%	$91.9805	$91.98	$92.00	$92.00
Purchase #7	$55.76	11.198%	$62.004	$62.00	$62.00	$62.00
7 purchase totals =	$843.78		$921.0157	$921.01	$921.05	$921.00