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	$123.43	7.841%	$133.1081	$133.11	$133.10	$133.10
Purchase #2	$83.36	7.503%	$89.6145	$89.61	$89.60	$89.60
Purchase #3	$168.96	11.522%	$188.4276	$188.43	$188.45	$188.40
Purchase #4	$203.81	13.506%	$231.3366	$231.34	$231.35	$231.30
Purchase #5	$53.29	4.552%	$55.7158	$55.72	$55.70	$55.70
Purchase #6	$124.60	13.417%	$141.3176	$141.32	$141.30	$141.30
Purchase #7	$42.83	10.580%	$47.3614	$47.36	$47.35	$47.40
7 purchase totals =	$800.28		$886.8816	$886.89	$886.85	$886.80