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	$28.94	10.642%	$32.0198	$32.02	$32.00	$32.00
Purchase #2	$210.43	10.755%	$233.0617	$233.06	$233.05	$233.10
Purchase #3	$8.53	4.767%	$8.9366	$8.94	$8.95	$8.90
Purchase #4	$12.53	12.170%	$14.0549	$14.05	$14.05	$14.10
Purchase #5	$219.95	13.700%	$250.0832	$250.08	$250.10	$250.10
Purchase #6	$31.89	6.232%	$33.8774	$33.88	$33.90	$33.90
Purchase #7	$249.68	12.335%	$280.478	$280.48	$280.50	$280.50
7 purchase totals =	$761.95		$852.5116	$852.51	$852.55	$852.60