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	$29.78	5.605%	$31.4492	$31.45	$31.45	$31.40
Purchase #2	$160.40	8.351%	$173.795	$173.80	$173.80	$173.80
Purchase #3	$89.96	11.538%	$100.3396	$100.34	$100.35	$100.30
Purchase #4	$232.53	11.759%	$259.8732	$259.87	$259.85	$259.90
Purchase #5	$128.37	11.288%	$142.8604	$142.86	$142.85	$142.90
Purchase #6	$170.48	4.667%	$178.4363	$178.44	$178.45	$178.40
Purchase #7	$79.65	3.459%	$82.4051	$82.41	$82.40	$82.40
7 purchase totals =	$891.17		$969.1588	$969.17	$969.15	$969.10