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	$134.76	11.434%	$150.1685	$150.17	$150.15	$150.20
Purchase #2	$83.90	9.460%	$91.8369	$91.84	$91.85	$91.80
Purchase #3	$29.30	3.795%	$30.4119	$30.41	$30.40	$30.40
Purchase #4	$7.55	12.735%	$8.5115	$8.51	$8.50	$8.50
Purchase #5	$83.92	6.379%	$89.2733	$89.27	$89.25	$89.30
Purchase #6	$245.66	6.427%	$261.4486	$261.45	$261.45	$261.40
Purchase #7	$133.54	9.747%	$146.5561	$146.56	$146.55	$146.60
7 purchase totals =	$718.63		$778.2068	$778.21	$778.15	$778.20