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	$98.43	6.154%	$104.4874	$104.49	$104.50	$104.50
Purchase #2	$72.46	11.280%	$80.6335	$80.63	$80.65	$80.60
Purchase #3	$58.74	11.461%	$65.4722	$65.47	$65.45	$65.50
Purchase #4	$245.56	8.329%	$266.0127	$266.01	$266.00	$266.00
Purchase #5	$248.81	12.419%	$279.7097	$279.71	$279.70	$279.70
Purchase #6	$166.28	7.826%	$179.2931	$179.29	$179.30	$179.30
Purchase #7	$16.93	8.172%	$18.3135	$18.31	$18.30	$18.30
7 purchase totals =	$907.21		$993.9221	$993.91	$993.90	$993.90