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	$99.37	4.654%	$103.9947	$103.99	$104.00	$104.00
Purchase #2	$191.38	12.521%	$215.3427	$215.34	$215.35	$215.30
Purchase #3	$96.66	10.640%	$106.9446	$106.94	$106.95	$106.90
Purchase #4	$104.30	13.384%	$118.2595	$118.26	$118.25	$118.30
Purchase #5	$27.89	7.289%	$29.9229	$29.92	$29.90	$29.90
Purchase #6	$115.27	6.754%	$123.0553	$123.06	$123.05	$123.10
Purchase #7	$225.73	7.445%	$242.5356	$242.54	$242.55	$242.50
7 purchase totals =	$860.60		$940.0553	$940.05	$940.05	$940.00