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	$229.40	12.544%	$258.1759	$258.18	$258.20	$258.20
Purchase #2	$129.80	5.457%	$136.8832	$136.88	$136.90	$136.90
Purchase #3	$123.38	6.677%	$131.6181	$131.62	$131.60	$131.60
Purchase #4	$37.90	11.120%	$42.1145	$42.11	$42.10	$42.10
Purchase #5	$94.48	11.826%	$105.6532	$105.65	$105.65	$105.70
Purchase #6	$81.78	9.551%	$89.5908	$89.59	$89.60	$89.60
Purchase #7	$154.31	11.185%	$171.5696	$171.57	$171.55	$171.60
7 purchase totals =	$851.05		$935.6053	$935.60	$935.60	$935.70