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	$57.71	7.300%	$61.9228	$61.92	$61.90	$61.90
Purchase #2	$93.71	6.386%	$99.6943	$99.69	$99.70	$99.70
Purchase #3	$237.90	7.316%	$255.3048	$255.30	$255.30	$255.30
Purchase #4	$6.84	10.870%	$7.5835	$7.58	$7.60	$7.60
Purchase #5	$116.34	4.130%	$121.1448	$121.14	$121.15	$121.10
Purchase #6	$69.51	3.592%	$72.0068	$72.01	$72.00	$72.00
Purchase #7	$198.81	6.817%	$212.3629	$212.36	$212.35	$212.40
7 purchase totals =	$780.82		$830.0199	$830.00	$830.00	$830.00