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	$53.72	6.543%	$57.2349	$57.23	$57.25	$57.20
Purchase #2	$235.79	13.573%	$267.7938	$267.79	$267.80	$267.80
Purchase #3	$144.58	8.524%	$156.904	$156.90	$156.90	$156.90
Purchase #4	$94.85	8.874%	$103.267	$103.27	$103.25	$103.30
Purchase #5	$179.57	3.134%	$185.1977	$185.20	$185.20	$185.20
Purchase #6	$80.63	10.528%	$89.1187	$89.12	$89.10	$89.10
Purchase #7	$202.90	13.750%	$230.7988	$230.80	$230.80	$230.80
7 purchase totals =	$992.04		$1,090.3149	$1,090.31	$1,090.30	$1,090.30