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	$87.76	13.224%	$99.3654	$99.37	$99.35	$99.40
Purchase #2	$28.58	10.374%	$31.5449	$31.54	$31.55	$31.50
Purchase #3	$110.41	3.524%	$114.3008	$114.30	$114.30	$114.30
Purchase #4	$182.39	5.845%	$193.0507	$193.05	$193.05	$193.10
Purchase #5	$76.98	10.836%	$85.3216	$85.32	$85.30	$85.30
Purchase #6	$51.27	6.443%	$54.5733	$54.57	$54.55	$54.60
Purchase #7	$111.50	9.337%	$121.9108	$121.91	$121.90	$121.90
7 purchase totals =	$648.89		$700.0675	$700.06	$700.00	$700.10