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	$83.29	12.139%	$93.4006	$93.40	$93.40	$93.40
Purchase #2	$123.62	3.382%	$127.8008	$127.80	$127.80	$127.80
Purchase #3	$222.25	9.422%	$243.1904	$243.19	$243.20	$243.20
Purchase #4	$238.32	3.610%	$246.9234	$246.92	$246.90	$246.90
Purchase #5	$80.27	7.790%	$86.523	$86.52	$86.50	$86.50
Purchase #6	$112.73	9.589%	$123.5397	$123.54	$123.55	$123.50
Purchase #7	$33.47	7.246%	$35.8952	$35.90	$35.90	$35.90
7 purchase totals =	$893.95		$957.2731	$957.27	$957.25	$957.20