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	$43.84	7.821%	$47.2687	$47.27	$47.25	$47.30
Purchase #2	$166.66	9.758%	$182.9227	$182.92	$182.90	$182.90
Purchase #3	$160.27	4.273%	$167.1183	$167.12	$167.10	$167.10
Purchase #4	$72.47	10.328%	$79.9547	$79.95	$79.95	$80.00
Purchase #5	$12.69	10.254%	$13.9912	$13.99	$14.00	$14.00
Purchase #6	$97.51	12.697%	$109.8908	$109.89	$109.90	$109.90
Purchase #7	$152.31	13.167%	$172.3647	$172.36	$172.35	$172.40
7 purchase totals =	$705.75		$773.5111	$773.50	$773.45	$773.60