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	$82.99	6.805%	$88.6375	$88.64	$88.65	$88.60
Purchase #2	$184.64	12.589%	$207.8843	$207.88	$207.90	$207.90
Purchase #3	$137.74	12.454%	$154.8941	$154.89	$154.90	$154.90
Purchase #4	$249.69	12.467%	$280.8189	$280.82	$280.80	$280.80
Purchase #5	$80.47	11.197%	$89.4802	$89.48	$89.50	$89.50
Purchase #6	$131.54	4.629%	$137.629	$137.63	$137.65	$137.60
Purchase #7	$19.30	8.403%	$20.9218	$20.92	$20.90	$20.90
7 purchase totals =	$886.37		$980.2658	$980.26	$980.30	$980.20