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	$223.51	8.862%	$243.3175	$243.32	$243.30	$243.30
Purchase #2	$64.96	12.305%	$72.9533	$72.95	$72.95	$73.00
Purchase #3	$248.80	5.866%	$263.3946	$263.39	$263.40	$263.40
Purchase #4	$45.82	11.512%	$51.0948	$51.09	$51.10	$51.10
Purchase #5	$109.35	13.160%	$123.7405	$123.74	$123.75	$123.70
Purchase #6	$169.46	12.745%	$191.0577	$191.06	$191.05	$191.10
Purchase #7	$76.76	11.842%	$85.8499	$85.85	$85.85	$85.80
7 purchase totals =	$938.66		$1,031.4083	$1,031.40	$1,031.40	$1,031.40