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	$85.71	6.284%	$91.096	$91.10	$91.10	$91.10
Purchase #2	$130.41	6.140%	$138.4172	$138.42	$138.40	$138.40
Purchase #3	$191.79	10.736%	$212.3806	$212.38	$212.40	$212.40
Purchase #4	$74.90	10.645%	$82.8731	$82.87	$82.85	$82.90
Purchase #5	$166.50	6.473%	$177.2775	$177.28	$177.30	$177.30
Purchase #6	$112.56	9.576%	$123.3387	$123.34	$123.35	$123.30
Purchase #7	$32.52	8.391%	$35.2488	$35.25	$35.25	$35.20
7 purchase totals =	$794.39		$860.6319	$860.64	$860.65	$860.60