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	$229.88	10.293%	$253.5415	$253.54	$253.55	$253.50
Purchase #2	$63.76	6.538%	$67.9286	$67.93	$67.95	$67.90
Purchase #3	$78.40	3.695%	$81.2969	$81.30	$81.30	$81.30
Purchase #4	$241.41	3.739%	$250.4363	$250.44	$250.45	$250.40
Purchase #5	$8.94	12.651%	$10.071	$10.07	$10.05	$10.10
Purchase #6	$183.91	6.870%	$196.5446	$196.54	$196.55	$196.50
Purchase #7	$74.52	5.673%	$78.7475	$78.75	$78.75	$78.70
7 purchase totals =	$880.82		$938.5664	$938.57	$938.60	$938.40