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	$90.44	11.151%	$100.525	$100.53	$100.55	$100.50
Purchase #2	$182.71	7.626%	$196.6435	$196.64	$196.65	$196.60
Purchase #3	$134.99	4.832%	$141.5127	$141.51	$141.50	$141.50
Purchase #4	$102.35	4.110%	$106.5566	$106.56	$106.55	$106.60
Purchase #5	$183.33	6.288%	$194.8578	$194.86	$194.85	$194.90
Purchase #6	$148.87	12.686%	$167.7556	$167.76	$167.75	$167.80
Purchase #7	$15.92	6.143%	$16.898	$16.90	$16.90	$16.90
7 purchase totals =	$858.61		$924.7492	$924.76	$924.75	$924.80