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	$59.54	8.437%	$64.5634	$64.56	$64.55	$64.60
Purchase #2	$225.70	10.831%	$250.1456	$250.15	$250.15	$250.10
Purchase #3	$191.52	6.691%	$204.3346	$204.33	$204.35	$204.30
Purchase #4	$36.85	6.855%	$39.3761	$39.38	$39.40	$39.40
Purchase #5	$164.39	3.357%	$169.9086	$169.91	$169.90	$169.90
Purchase #6	$73.48	9.675%	$80.5892	$80.59	$80.60	$80.60
Purchase #7	$176.71	12.375%	$198.5779	$198.58	$198.60	$198.60
7 purchase totals =	$928.19		$1,007.4954	$1,007.50	$1,007.55	$1,007.50