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	$179.79	12.144%	$201.6237	$201.62	$201.60	$201.60
Purchase #2	$110.41	7.312%	$118.4832	$118.48	$118.50	$118.50
Purchase #3	$150.77	13.749%	$171.4994	$171.50	$171.50	$171.50
Purchase #4	$116.76	6.659%	$124.535	$124.54	$124.55	$124.50
Purchase #5	$14.30	6.814%	$15.2744	$15.27	$15.25	$15.30
Purchase #6	$70.38	11.666%	$78.5905	$78.59	$78.60	$78.60
Purchase #7	$171.98	10.681%	$190.3492	$190.35	$190.35	$190.30
7 purchase totals =	$814.39		$900.3554	$900.35	$900.35	$900.30