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	$41.45	13.842%	$47.1875	$47.19	$47.20	$47.20
Purchase #2	$194.82	4.828%	$204.2259	$204.23	$204.25	$204.20
Purchase #3	$180.25	12.550%	$202.8714	$202.87	$202.85	$202.90
Purchase #4	$81.48	9.640%	$89.3347	$89.33	$89.35	$89.30
Purchase #5	$250.60	12.489%	$281.8974	$281.90	$281.90	$281.90
Purchase #6	$42.39	6.791%	$45.2687	$45.27	$45.25	$45.30
Purchase #7	$192.72	6.407%	$205.0676	$205.07	$205.05	$205.10
7 purchase totals =	$983.71		$1,075.8532	$1,075.86	$1,075.85	$1,075.90