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	$46.82	9.471%	$51.2543	$51.25	$51.25	$51.30
Purchase #2	$135.76	10.699%	$150.285	$150.29	$150.30	$150.30
Purchase #3	$211.57	11.331%	$235.543	$235.54	$235.55	$235.50
Purchase #4	$95.41	11.494%	$106.3764	$106.38	$106.40	$106.40
Purchase #5	$184.25	4.675%	$192.8637	$192.86	$192.85	$192.90
Purchase #6	$35.45	12.513%	$39.8859	$39.89	$39.90	$39.90
Purchase #7	$62.82	3.815%	$65.2166	$65.22	$65.20	$65.20
7 purchase totals =	$772.08		$841.4249	$841.43	$841.45	$841.50