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	$135.89	8.611%	$147.5915	$147.59	$147.60	$147.60
Purchase #2	$179.39	3.635%	$185.9108	$185.91	$185.90	$185.90
Purchase #3	$158.40	12.561%	$178.2966	$178.30	$178.30	$178.30
Purchase #4	$245.28	12.298%	$275.4445	$275.44	$275.45	$275.40
Purchase #5	$34.26	12.698%	$38.6103	$38.61	$38.60	$38.60
Purchase #6	$189.49	3.719%	$196.5371	$196.54	$196.55	$196.50
Purchase #7	$203.79	7.121%	$218.3019	$218.30	$218.30	$218.30
7 purchase totals =	$1,146.50		$1,240.6927	$1,240.69	$1,240.70	$1,240.60