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	$76.63	3.846%	$79.5772	$79.58	$79.60	$79.60
Purchase #2	$165.58	11.621%	$184.8221	$184.82	$184.80	$184.80
Purchase #3	$17.70	3.451%	$18.3108	$18.31	$18.30	$18.30
Purchase #4	$135.91	3.329%	$140.4344	$140.43	$140.45	$140.40
Purchase #5	$101.47	7.518%	$109.0985	$109.10	$109.10	$109.10
Purchase #6	$83.78	10.837%	$92.8592	$92.86	$92.85	$92.90
Purchase #7	$35.32	9.148%	$38.5511	$38.55	$38.55	$38.60
7 purchase totals =	$616.39		$663.6533	$663.65	$663.65	$663.70