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	$55.51	13.795%	$63.1676	$63.17	$63.15	$63.20
Purchase #2	$41.96	9.293%	$45.8593	$45.86	$45.85	$45.90
Purchase #3	$210.29	12.836%	$237.2828	$237.28	$237.30	$237.30
Purchase #4	$201.73	5.700%	$213.2286	$213.23	$213.25	$213.20
Purchase #5	$156.54	5.559%	$165.2421	$165.24	$165.25	$165.20
Purchase #6	$158.54	9.719%	$173.9485	$173.95	$173.95	$173.90
Purchase #7	$86.98	4.223%	$90.6532	$90.65	$90.65	$90.70
7 purchase totals =	$911.55		$989.3821	$989.38	$989.40	$989.40