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	$171.58	8.243%	$185.7233	$185.72	$185.70	$185.70
Purchase #2	$202.72	5.190%	$213.2412	$213.24	$213.25	$213.20
Purchase #3	$81.45	6.735%	$86.9357	$86.94	$86.95	$86.90
Purchase #4	$157.37	8.697%	$171.0565	$171.06	$171.05	$171.10
Purchase #5	$126.72	9.319%	$138.529	$138.53	$138.55	$138.50
Purchase #6	$82.28	3.676%	$85.3046	$85.30	$85.30	$85.30
Purchase #7	$78.80	13.844%	$89.7091	$89.71	$89.70	$89.70
7 purchase totals =	$900.92		$970.4994	$970.50	$970.50	$970.40