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	$191.64	3.700%	$198.7307	$198.73	$198.75	$198.70
Purchase #2	$36.48	5.372%	$38.4397	$38.44	$38.45	$38.40
Purchase #3	$99.77	9.676%	$109.4237	$109.42	$109.40	$109.40
Purchase #4	$57.95	7.614%	$62.3623	$62.36	$62.35	$62.40
Purchase #5	$38.47	11.606%	$42.9348	$42.93	$42.95	$42.90
Purchase #6	$56.29	8.682%	$61.1771	$61.18	$61.20	$61.20
Purchase #7	$139.88	11.130%	$155.4486	$155.45	$155.45	$155.40
7 purchase totals =	$620.48		$668.5169	$668.51	$668.55	$668.40