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	$93.78	7.545%	$100.8557	$100.86	$100.85	$100.90
Purchase #2	$161.42	11.517%	$180.0107	$180.01	$180.00	$180.00
Purchase #3	$67.70	12.655%	$76.2674	$76.27	$76.25	$76.30
Purchase #4	$60.56	3.774%	$62.8455	$62.85	$62.85	$62.80
Purchase #5	$88.91	11.692%	$99.3054	$99.31	$99.30	$99.30
Purchase #6	$59.64	10.459%	$65.8777	$65.88	$65.90	$65.90
Purchase #7	$73.81	12.497%	$83.034	$83.03	$83.05	$83.00
7 purchase totals =	$605.82		$668.1964	$668.21	$668.20	$668.20