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	$78.28	13.713%	$89.0145	$89.01	$89.00	$89.00
Purchase #2	$196.73	4.381%	$205.3487	$205.35	$205.35	$205.30
Purchase #3	$144.47	10.308%	$159.362	$159.36	$159.35	$159.40
Purchase #4	$232.46	9.801%	$255.2434	$255.24	$255.25	$255.20
Purchase #5	$72.97	13.315%	$82.686	$82.69	$82.70	$82.70
Purchase #6	$58.76	7.109%	$62.9372	$62.94	$62.95	$62.90
Purchase #7	$187.30	5.372%	$197.3618	$197.36	$197.35	$197.40
7 purchase totals =	$970.97		$1,051.9536	$1,051.95	$1,051.95	$1,051.90