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	$103.63	11.142%	$115.1765	$115.18	$115.20	$115.20
Purchase #2	$241.66	3.666%	$250.5193	$250.52	$250.50	$250.50
Purchase #3	$198.40	12.688%	$223.573	$223.57	$223.55	$223.60
Purchase #4	$161.56	4.578%	$168.9562	$168.96	$168.95	$169.00
Purchase #5	$160.34	11.538%	$178.84	$178.84	$178.85	$178.80
Purchase #6	$31.43	11.339%	$34.9938	$34.99	$35.00	$35.00
Purchase #7	$80.55	10.806%	$89.2542	$89.25	$89.25	$89.30
7 purchase totals =	$977.57		$1,061.3130	$1,061.31	$1,061.30	$1,061.40