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	$91.75	12.822%	$103.5142	$103.51	$103.50	$103.50
Purchase #2	$243.42	10.398%	$268.7308	$268.73	$268.75	$268.70
Purchase #3	$53.53	10.736%	$59.277	$59.28	$59.30	$59.30
Purchase #4	$174.42	9.841%	$191.5847	$191.58	$191.60	$191.60
Purchase #5	$194.47	11.742%	$217.3047	$217.30	$217.30	$217.30
Purchase #6	$116.28	6.223%	$123.5161	$123.52	$123.50	$123.50
Purchase #7	$218.66	9.213%	$238.8051	$238.81	$238.80	$238.80
7 purchase totals =	$1,092.53		$1,202.7326	$1,202.73	$1,202.75	$1,202.70