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	$10.98	13.234%	$12.4331	$12.43	$12.45	$12.40
Purchase #2	$47.98	8.132%	$51.8817	$51.88	$51.90	$51.90
Purchase #3	$82.70	9.254%	$90.3531	$90.35	$90.35	$90.40
Purchase #4	$173.86	6.842%	$185.7555	$185.76	$185.75	$185.80
Purchase #5	$27.48	13.629%	$31.2252	$31.23	$31.25	$31.20
Purchase #6	$23.52	13.559%	$26.7091	$26.71	$26.70	$26.70
Purchase #7	$224.33	6.334%	$238.5391	$238.54	$238.55	$238.50
7 purchase totals =	$590.85		$636.8968	$636.90	$636.95	$636.90