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	$119.55	7.158%	$128.1074	$128.11	$128.10	$128.10
Purchase #2	$37.29	4.369%	$38.9192	$38.92	$38.90	$38.90
Purchase #3	$165.80	13.646%	$188.4251	$188.43	$188.45	$188.40
Purchase #4	$122.84	10.811%	$136.1202	$136.12	$136.10	$136.10
Purchase #5	$108.56	13.787%	$123.5272	$123.53	$123.55	$123.50
Purchase #6	$87.33	10.131%	$96.1774	$96.18	$96.20	$96.20
Purchase #7	$177.80	7.300%	$190.7794	$190.78	$190.80	$190.80
7 purchase totals =	$819.17		$902.0559	$902.07	$902.10	$902.00