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	$110.44	5.787%	$116.8312	$116.83	$116.85	$116.80
Purchase #2	$86.91	12.425%	$97.7086	$97.71	$97.70	$97.70
Purchase #3	$98.78	10.672%	$109.3218	$109.32	$109.30	$109.30
Purchase #4	$12.78	4.320%	$13.3321	$13.33	$13.35	$13.30
Purchase #5	$40.87	6.835%	$43.6635	$43.66	$43.65	$43.70
Purchase #6	$73.68	12.679%	$83.0219	$83.02	$83.00	$83.00
Purchase #7	$221.31	12.537%	$249.0556	$249.06	$249.05	$249.10
7 purchase totals =	$644.77		$712.9347	$712.93	$712.90	$712.90