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	$128.70	8.317%	$139.404	$139.40	$139.40	$139.40
Purchase #2	$227.69	12.671%	$256.5406	$256.54	$256.55	$256.50
Purchase #3	$78.43	10.410%	$86.5946	$86.59	$86.60	$86.60
Purchase #4	$240.38	9.793%	$263.9204	$263.92	$263.90	$263.90
Purchase #5	$76.73	3.562%	$79.4631	$79.46	$79.45	$79.50
Purchase #6	$77.72	9.118%	$84.8065	$84.81	$84.80	$84.80
Purchase #7	$29.57	13.677%	$33.6143	$33.61	$33.60	$33.60
7 purchase totals =	$859.22		$944.3435	$944.33	$944.30	$944.30