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	$180.40	5.543%	$190.3996	$190.40	$190.40	$190.40
Purchase #2	$194.33	11.627%	$216.9247	$216.92	$216.90	$216.90
Purchase #3	$167.38	13.371%	$189.7604	$189.76	$189.75	$189.80
Purchase #4	$187.30	12.158%	$210.0719	$210.07	$210.05	$210.10
Purchase #5	$108.43	12.260%	$121.7235	$121.72	$121.70	$121.70
Purchase #6	$184.39	5.519%	$194.5665	$194.57	$194.55	$194.60
Purchase #7	$170.29	12.693%	$191.9049	$191.90	$191.90	$191.90
7 purchase totals =	$1,192.52		$1,315.3515	$1,315.34	$1,315.25	$1,315.40