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	$242.46	5.687%	$256.2487	$256.25	$256.25	$256.20
Purchase #2	$146.52	12.338%	$164.5976	$164.60	$164.60	$164.60
Purchase #3	$184.28	4.154%	$191.935	$191.94	$191.95	$191.90
Purchase #4	$165.54	3.619%	$171.5309	$171.53	$171.55	$171.50
Purchase #5	$135.34	3.341%	$139.8617	$139.86	$139.85	$139.90
Purchase #6	$197.77	4.562%	$206.7923	$206.79	$206.80	$206.80
Purchase #7	$192.58	4.263%	$200.7897	$200.79	$200.80	$200.80
7 purchase totals =	$1,264.49		$1,331.7559	$1,331.76	$1,331.80	$1,331.70