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	$77.80	5.341%	$81.9553	$81.96	$81.95	$82.00
Purchase #2	$83.89	7.355%	$90.0601	$90.06	$90.05	$90.10
Purchase #3	$130.36	8.721%	$141.7287	$141.73	$141.75	$141.70
Purchase #4	$136.98	10.479%	$151.3341	$151.33	$151.35	$151.30
Purchase #5	$61.48	13.648%	$69.8708	$69.87	$69.85	$69.90
Purchase #6	$138.92	13.814%	$158.1104	$158.11	$158.10	$158.10
Purchase #7	$94.56	6.478%	$100.6856	$100.69	$100.70	$100.70
7 purchase totals =	$723.99		$793.7450	$793.75	$793.75	$793.80