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	$72.40	8.577%	$78.6097	$78.61	$78.60	$78.60
Purchase #2	$93.79	9.404%	$102.61	$102.61	$102.60	$102.60
Purchase #3	$116.47	12.705%	$131.2675	$131.27	$131.25	$131.30
Purchase #4	$185.90	9.645%	$203.8301	$203.83	$203.85	$203.80
Purchase #5	$79.56	13.708%	$90.4661	$90.47	$90.45	$90.50
Purchase #6	$245.51	13.117%	$277.7135	$277.71	$277.70	$277.70
Purchase #7	$115.62	10.864%	$128.181	$128.18	$128.20	$128.20
7 purchase totals =	$909.25		$1,012.6779	$1,012.68	$1,012.65	$1,012.70