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	$129.73	5.696%	$137.1194	$137.12	$137.10	$137.10
Purchase #2	$236.59	9.855%	$259.9059	$259.91	$259.90	$259.90
Purchase #3	$72.43	8.468%	$78.5634	$78.56	$78.55	$78.60
Purchase #4	$223.91	10.789%	$248.0676	$248.07	$248.05	$248.10
Purchase #5	$63.89	3.494%	$66.1223	$66.12	$66.10	$66.10
Purchase #6	$86.54	5.234%	$91.0695	$91.07	$91.05	$91.10
Purchase #7	$120.57	13.746%	$137.1436	$137.14	$137.15	$137.10
7 purchase totals =	$933.66		$1,017.9917	$1,017.99	$1,017.90	$1,018.00