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	$112.52	3.396%	$116.3412	$116.34	$116.35	$116.30
Purchase #2	$83.81	7.365%	$89.9826	$89.98	$90.00	$90.00
Purchase #3	$51.58	7.709%	$55.5563	$55.56	$55.55	$55.60
Purchase #4	$46.66	10.341%	$51.4851	$51.49	$51.50	$51.50
Purchase #5	$133.87	13.721%	$152.2383	$152.24	$152.25	$152.20
Purchase #6	$52.76	6.166%	$56.0132	$56.01	$56.00	$56.00
Purchase #7	$72.36	7.817%	$78.0164	$78.02	$78.00	$78.00
7 purchase totals =	$553.56		$599.6331	$599.64	$599.65	$599.60