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	$81.85	13.701%	$93.0643	$93.06	$93.05	$93.10
Purchase #2	$29.57	6.842%	$31.5932	$31.59	$31.60	$31.60
Purchase #3	$48.91	11.640%	$54.6031	$54.60	$54.60	$54.60
Purchase #4	$206.39	11.317%	$229.7472	$229.75	$229.75	$229.70
Purchase #5	$103.98	9.207%	$113.5534	$113.55	$113.55	$113.60
Purchase #6	$90.48	9.802%	$99.3488	$99.35	$99.35	$99.30
Purchase #7	$59.72	6.598%	$63.6603	$63.66	$63.65	$63.70
7 purchase totals =	$620.90		$685.5703	$685.56	$685.55	$685.60