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	$103.51	9.109%	$112.9387	$112.94	$112.95	$112.90
Purchase #2	$118.98	9.525%	$130.3128	$130.31	$130.30	$130.30
Purchase #3	$242.77	11.298%	$270.1982	$270.20	$270.20	$270.20
Purchase #4	$109.70	12.773%	$123.712	$123.71	$123.70	$123.70
Purchase #5	$41.34	4.459%	$43.1834	$43.18	$43.20	$43.20
Purchase #6	$236.49	13.869%	$269.2888	$269.29	$269.30	$269.30
Purchase #7	$219.98	9.702%	$241.3225	$241.32	$241.30	$241.30
7 purchase totals =	$1,072.77		$1,190.9564	$1,190.95	$1,190.95	$1,190.90