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	$73.89	12.808%	$83.3538	$83.35	$83.35	$83.40
Purchase #2	$84.29	3.360%	$87.1221	$87.12	$87.10	$87.10
Purchase #3	$160.42	11.429%	$178.7544	$178.75	$178.75	$178.80
Purchase #4	$173.34	13.228%	$196.2694	$196.27	$196.25	$196.30
Purchase #5	$118.64	5.473%	$125.1332	$125.13	$125.15	$125.10
Purchase #6	$86.89	3.425%	$89.866	$89.87	$89.85	$89.90
Purchase #7	$201.96	13.837%	$229.9052	$229.91	$229.90	$229.90
7 purchase totals =	$899.43		$990.4041	$990.40	$990.35	$990.50