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	$218.30	9.635%	$239.3332	$239.33	$239.35	$239.30
Purchase #2	$64.37	3.374%	$66.5418	$66.54	$66.55	$66.50
Purchase #3	$234.47	6.362%	$249.387	$249.39	$249.40	$249.40
Purchase #4	$83.82	9.421%	$91.7167	$91.72	$91.70	$91.70
Purchase #5	$108.63	10.433%	$119.9634	$119.96	$119.95	$120.00
Purchase #6	$69.48	13.442%	$78.8195	$78.82	$78.80	$78.80
Purchase #7	$115.78	13.328%	$131.2112	$131.21	$131.20	$131.20
7 purchase totals =	$894.85		$976.9728	$976.97	$976.95	$976.90