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	$80.73	11.804%	$90.2594	$90.26	$90.25	$90.30
Purchase #2	$116.84	9.637%	$128.0999	$128.10	$128.10	$128.10
Purchase #3	$209.33	6.218%	$222.3461	$222.35	$222.35	$222.30
Purchase #4	$182.64	3.438%	$188.9192	$188.92	$188.90	$188.90
Purchase #5	$233.89	4.498%	$244.4104	$244.41	$244.40	$244.40
Purchase #6	$130.83	9.481%	$143.234	$143.23	$143.25	$143.20
Purchase #7	$246.52	13.701%	$280.2957	$280.30	$280.30	$280.30
7 purchase totals =	$1,200.78		$1,297.5647	$1,297.57	$1,297.55	$1,297.50