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	$124.41	4.393%	$129.8753	$129.88	$129.90	$129.90
Purchase #2	$131.95	12.645%	$148.6351	$148.64	$148.65	$148.60
Purchase #3	$73.33	12.154%	$82.2425	$82.24	$82.25	$82.20
Purchase #4	$105.71	3.789%	$109.7154	$109.72	$109.70	$109.70
Purchase #5	$71.75	12.611%	$80.7984	$80.80	$80.80	$80.80
Purchase #6	$39.64	12.543%	$44.612	$44.61	$44.60	$44.60
Purchase #7	$151.36	11.365%	$168.5621	$168.56	$168.55	$168.60
7 purchase totals =	$698.15		$764.4408	$764.45	$764.45	$764.40