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	$78.59	13.510%	$89.2075	$89.21	$89.20	$89.20
Purchase #2	$185.31	5.873%	$196.1933	$196.19	$196.20	$196.20
Purchase #3	$171.70	8.356%	$186.0473	$186.05	$186.05	$186.00
Purchase #4	$58.56	5.504%	$61.7831	$61.78	$61.80	$61.80
Purchase #5	$39.79	3.851%	$41.3223	$41.32	$41.30	$41.30
Purchase #6	$85.93	3.321%	$88.7837	$88.78	$88.80	$88.80
Purchase #7	$221.80	8.407%	$240.4467	$240.45	$240.45	$240.40
7 purchase totals =	$841.68		$903.7839	$903.78	$903.80	$903.70