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	$84.81	6.506%	$90.3277	$90.33	$90.35	$90.30
Purchase #2	$235.52	3.523%	$243.8174	$243.82	$243.80	$243.80
Purchase #3	$91.34	13.141%	$103.343	$103.34	$103.35	$103.30
Purchase #4	$201.61	3.437%	$208.5393	$208.54	$208.55	$208.50
Purchase #5	$36.77	9.383%	$40.2201	$40.22	$40.20	$40.20
Purchase #6	$62.53	5.231%	$65.8009	$65.80	$65.80	$65.80
Purchase #7	$171.88	3.210%	$177.3973	$177.40	$177.40	$177.40
7 purchase totals =	$884.46		$929.4457	$929.45	$929.45	$929.30