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	$26.34	13.485%	$29.8919	$29.89	$29.90	$29.90
Purchase #2	$95.27	4.113%	$99.1885	$99.19	$99.20	$99.20
Purchase #3	$242.65	8.488%	$263.2461	$263.25	$263.25	$263.20
Purchase #4	$54.86	4.319%	$57.2294	$57.23	$57.25	$57.20
Purchase #5	$152.26	8.277%	$164.8626	$164.86	$164.85	$164.90
Purchase #6	$110.92	4.464%	$115.8715	$115.87	$115.85	$115.90
Purchase #7	$178.59	13.803%	$203.2408	$203.24	$203.25	$203.20
7 purchase totals =	$860.89		$933.5308	$933.53	$933.55	$933.50