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	$21.43	3.470%	$22.1736	$22.17	$22.15	$22.20
Purchase #2	$224.79	10.490%	$248.3705	$248.37	$248.35	$248.40
Purchase #3	$86.98	12.811%	$98.123	$98.12	$98.10	$98.10
Purchase #4	$130.85	8.615%	$142.1227	$142.12	$142.10	$142.10
Purchase #5	$227.77	4.535%	$238.0994	$238.10	$238.10	$238.10
Purchase #6	$136.79	4.211%	$142.5502	$142.55	$142.55	$142.60
Purchase #7	$96.34	4.148%	$100.3362	$100.34	$100.35	$100.30
7 purchase totals =	$924.95		$991.7756	$991.77	$991.70	$991.80