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	$175.43	3.111%	$180.8876	$180.89	$180.90	$180.90
Purchase #2	$163.88	5.570%	$173.0081	$173.01	$173.00	$173.00
Purchase #3	$83.32	3.159%	$85.9521	$85.95	$85.95	$86.00
Purchase #4	$65.97	11.735%	$73.7116	$73.71	$73.70	$73.70
Purchase #5	$86.72	11.539%	$96.7266	$96.73	$96.75	$96.70
Purchase #6	$69.55	4.416%	$72.6213	$72.62	$72.60	$72.60
Purchase #7	$175.47	7.511%	$188.6496	$188.65	$188.65	$188.60
7 purchase totals =	$820.34		$871.5569	$871.56	$871.55	$871.50