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	$109.49	8.582%	$118.8864	$118.89	$118.90	$118.90
Purchase #2	$120.62	13.227%	$136.5744	$136.57	$136.55	$136.60
Purchase #3	$146.25	7.575%	$157.3284	$157.33	$157.35	$157.30
Purchase #4	$129.72	6.312%	$137.9079	$137.91	$137.90	$137.90
Purchase #5	$35.80	8.646%	$38.8953	$38.90	$38.90	$38.90
Purchase #6	$93.56	11.171%	$104.0116	$104.01	$104.00	$104.00
Purchase #7	$76.41	13.682%	$86.8644	$86.86	$86.85	$86.90
7 purchase totals =	$711.85		$780.4684	$780.47	$780.45	$780.50