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	$84.78	3.403%	$87.6651	$87.67	$87.65	$87.70
Purchase #2	$189.54	12.141%	$212.5521	$212.55	$212.55	$212.60
Purchase #3	$79.72	13.466%	$90.4551	$90.46	$90.45	$90.50
Purchase #4	$191.77	12.174%	$215.1161	$215.12	$215.10	$215.10
Purchase #5	$167.99	7.216%	$180.1122	$180.11	$180.10	$180.10
Purchase #6	$84.78	5.378%	$89.3395	$89.34	$89.35	$89.30
Purchase #7	$90.86	11.265%	$101.0954	$101.10	$101.10	$101.10
7 purchase totals =	$889.44		$976.3355	$976.35	$976.30	$976.40