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	$140.48	8.586%	$152.5416	$152.54	$152.55	$152.50
Purchase #2	$33.57	6.161%	$35.6382	$35.64	$35.65	$35.60
Purchase #3	$155.84	4.489%	$162.8357	$162.84	$162.85	$162.80
Purchase #4	$93.34	7.385%	$100.2332	$100.23	$100.25	$100.20
Purchase #5	$131.51	3.793%	$136.4982	$136.50	$136.50	$136.50
Purchase #6	$238.46	4.215%	$248.5111	$248.51	$248.50	$248.50
Purchase #7	$141.70	9.176%	$154.7024	$154.70	$154.70	$154.70
7 purchase totals =	$934.90		$990.9604	$990.96	$991.00	$990.80