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	$159.64	13.442%	$181.0988	$181.10	$181.10	$181.10
Purchase #2	$183.36	7.314%	$196.771	$196.77	$196.75	$196.80
Purchase #3	$91.43	8.234%	$98.9583	$98.96	$98.95	$99.00
Purchase #4	$49.87	13.352%	$56.5286	$56.53	$56.55	$56.50
Purchase #5	$85.35	5.118%	$89.7182	$89.72	$89.70	$89.70
Purchase #6	$134.57	3.548%	$139.3445	$139.34	$139.35	$139.30
Purchase #7	$82.32	10.425%	$90.9019	$90.90	$90.90	$90.90
7 purchase totals =	$786.54		$853.3213	$853.32	$853.30	$853.30