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	$11.38	13.589%	$12.9264	$12.93	$12.95	$12.90
Purchase #2	$82.30	9.681%	$90.2675	$90.27	$90.25	$90.30
Purchase #3	$206.83	4.400%	$215.9305	$215.93	$215.95	$215.90
Purchase #4	$171.52	13.517%	$194.7044	$194.70	$194.70	$194.70
Purchase #5	$85.47	4.814%	$89.5845	$89.58	$89.60	$89.60
Purchase #6	$50.71	6.171%	$53.8393	$53.84	$53.85	$53.80
Purchase #7	$81.36	8.779%	$88.5026	$88.50	$88.50	$88.50
7 purchase totals =	$689.57		$745.7552	$745.75	$745.80	$745.70