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	$56.96	13.220%	$64.4901	$64.49	$64.50	$64.50
Purchase #2	$218.48	8.621%	$237.3152	$237.32	$237.30	$237.30
Purchase #3	$239.33	9.685%	$262.5091	$262.51	$262.50	$262.50
Purchase #4	$171.95	6.796%	$183.6357	$183.64	$183.65	$183.60
Purchase #5	$82.77	10.322%	$91.3135	$91.31	$91.30	$91.30
Purchase #6	$136.27	8.477%	$147.8216	$147.82	$147.80	$147.80
Purchase #7	$152.64	3.857%	$158.5273	$158.53	$158.55	$158.50
7 purchase totals =	$1,058.40		$1,145.6125	$1,145.62	$1,145.60	$1,145.50