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	$243.90	9.552%	$267.1973	$267.20	$267.20	$267.20
Purchase #2	$61.48	9.855%	$67.5389	$67.54	$67.55	$67.50
Purchase #3	$136.37	5.168%	$143.4176	$143.42	$143.40	$143.40
Purchase #4	$88.80	8.583%	$96.4217	$96.42	$96.40	$96.40
Purchase #5	$243.77	5.214%	$256.4802	$256.48	$256.50	$256.50
Purchase #6	$32.66	9.323%	$35.7049	$35.70	$35.70	$35.70
Purchase #7	$82.26	9.126%	$89.767	$89.77	$89.75	$89.80
7 purchase totals =	$889.24		$956.5276	$956.53	$956.50	$956.50