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	$29.59	11.200%	$32.9041	$32.90	$32.90	$32.90
Purchase #2	$136.34	7.112%	$146.0365	$146.04	$146.05	$146.00
Purchase #3	$79.51	12.608%	$89.5346	$89.53	$89.55	$89.50
Purchase #4	$5.98	8.802%	$6.5064	$6.51	$6.50	$6.50
Purchase #5	$135.48	13.807%	$154.1857	$154.19	$154.20	$154.20
Purchase #6	$103.46	4.416%	$108.0288	$108.03	$108.05	$108.00
Purchase #7	$62.35	7.539%	$67.0506	$67.05	$67.05	$67.10
7 purchase totals =	$552.71		$604.2467	$604.25	$604.30	$604.20