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	$25.38	12.753%	$28.6167	$28.62	$28.60	$28.60
Purchase #2	$135.30	12.398%	$152.0745	$152.07	$152.05	$152.10
Purchase #3	$29.28	6.736%	$31.2523	$31.25	$31.25	$31.30
Purchase #4	$137.34	6.222%	$145.8853	$145.89	$145.90	$145.90
Purchase #5	$230.85	6.873%	$246.7163	$246.72	$246.70	$246.70
Purchase #6	$225.51	8.835%	$245.4338	$245.43	$245.45	$245.40
Purchase #7	$43.90	6.828%	$46.8975	$46.90	$46.90	$46.90
7 purchase totals =	$827.56		$896.8764	$896.88	$896.85	$896.90