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	$107.34	10.786%	$118.9177	$118.92	$118.90	$118.90
Purchase #2	$153.88	10.270%	$169.6835	$169.68	$169.70	$169.70
Purchase #3	$105.79	13.431%	$119.9987	$120.00	$120.00	$120.00
Purchase #4	$202.69	9.753%	$222.4584	$222.46	$222.45	$222.50
Purchase #5	$139.54	12.135%	$156.4732	$156.47	$156.45	$156.50
Purchase #6	$158.98	7.244%	$170.4965	$170.50	$170.50	$170.50
Purchase #7	$20.51	3.830%	$21.2955	$21.30	$21.30	$21.30
7 purchase totals =	$888.73		$979.3235	$979.33	$979.30	$979.40