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	$212.44	6.255%	$225.7281	$225.73	$225.75	$225.70
Purchase #2	$132.82	6.111%	$140.9366	$140.94	$140.95	$140.90
Purchase #3	$67.74	5.125%	$71.2117	$71.21	$71.20	$71.20
Purchase #4	$100.56	9.212%	$109.8236	$109.82	$109.80	$109.80
Purchase #5	$45.73	5.710%	$48.3412	$48.34	$48.35	$48.30
Purchase #6	$53.95	10.303%	$59.5085	$59.51	$59.50	$59.50
Purchase #7	$245.68	12.518%	$276.4342	$276.43	$276.45	$276.40
7 purchase totals =	$858.92		$931.9839	$931.98	$932.00	$931.80