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	$79.75	12.405%	$89.643	$89.64	$89.65	$89.60
Purchase #2	$221.34	8.647%	$240.4793	$240.48	$240.50	$240.50
Purchase #3	$95.87	8.809%	$104.3152	$104.32	$104.30	$104.30
Purchase #4	$215.72	12.649%	$243.0064	$243.01	$243.00	$243.00
Purchase #5	$194.89	9.661%	$213.7183	$213.72	$213.70	$213.70
Purchase #6	$238.99	10.443%	$263.9477	$263.95	$263.95	$263.90
Purchase #7	$91.73	9.355%	$100.3113	$100.31	$100.30	$100.30
7 purchase totals =	$1,138.29		$1,255.4212	$1,255.43	$1,255.40	$1,255.30