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	$232.58	7.731%	$250.5608	$250.56	$250.55	$250.60
Purchase #2	$233.55	6.226%	$248.0908	$248.09	$248.10	$248.10
Purchase #3	$78.63	12.652%	$88.5783	$88.58	$88.60	$88.60
Purchase #4	$85.55	6.222%	$90.8729	$90.87	$90.85	$90.90
Purchase #5	$62.64	12.227%	$70.299	$70.30	$70.30	$70.30
Purchase #6	$248.71	7.200%	$266.6171	$266.62	$266.60	$266.60
Purchase #7	$40.85	4.411%	$42.6519	$42.65	$42.65	$42.70
7 purchase totals =	$982.51		$1,057.6708	$1,057.67	$1,057.65	$1,057.80