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	$227.95	13.621%	$258.9991	$259.00	$259.00	$259.00
Purchase #2	$249.53	3.777%	$258.9547	$258.95	$258.95	$259.00
Purchase #3	$168.98	9.486%	$185.0094	$185.01	$185.00	$185.00
Purchase #4	$130.39	3.564%	$135.0371	$135.04	$135.05	$135.00
Purchase #5	$92.31	8.774%	$100.4093	$100.41	$100.40	$100.40
Purchase #6	$181.30	8.550%	$196.8012	$196.80	$196.80	$196.80
Purchase #7	$181.32	5.723%	$191.6969	$191.70	$191.70	$191.70
7 purchase totals =	$1,231.78		$1,326.9077	$1,326.91	$1,326.90	$1,326.90