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	$35.76	5.574%	$37.7533	$37.75	$37.75	$37.80
Purchase #2	$215.38	9.476%	$235.7894	$235.79	$235.80	$235.80
Purchase #3	$105.47	13.319%	$119.5175	$119.52	$119.50	$119.50
Purchase #4	$122.69	8.410%	$133.0082	$133.01	$133.00	$133.00
Purchase #5	$55.66	10.173%	$61.3223	$61.32	$61.30	$61.30
Purchase #6	$79.39	3.678%	$82.31	$82.31	$82.30	$82.30
Purchase #7	$90.93	13.411%	$103.1246	$103.12	$103.10	$103.10
7 purchase totals =	$705.28		$772.8253	$772.82	$772.75	$772.80