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	$99.27	5.518%	$104.7477	$104.75	$104.75	$104.70
Purchase #2	$139.97	6.711%	$149.3634	$149.36	$149.35	$149.40
Purchase #3	$110.25	12.314%	$123.8262	$123.83	$123.85	$123.80
Purchase #4	$158.91	10.280%	$175.2459	$175.25	$175.25	$175.20
Purchase #5	$80.28	11.306%	$89.3565	$89.36	$89.35	$89.40
Purchase #6	$41.35	6.265%	$43.9406	$43.94	$43.95	$43.90
Purchase #7	$103.67	5.842%	$109.7264	$109.73	$109.75	$109.70
7 purchase totals =	$733.70		$796.2067	$796.22	$796.25	$796.10