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	$51.48	4.331%	$53.7096	$53.71	$53.70	$53.70
Purchase #2	$29.33	13.852%	$33.3928	$33.39	$33.40	$33.40
Purchase #3	$86.84	11.651%	$96.9577	$96.96	$96.95	$97.00
Purchase #4	$194.53	9.754%	$213.5045	$213.50	$213.50	$213.50
Purchase #5	$107.63	13.807%	$122.4905	$122.49	$122.50	$122.50
Purchase #6	$85.64	4.778%	$89.7319	$89.73	$89.75	$89.70
Purchase #7	$50.64	10.132%	$55.7708	$55.77	$55.75	$55.80
7 purchase totals =	$606.09		$665.5578	$665.55	$665.55	$665.60