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	$245.63	12.118%	$275.3954	$275.40	$275.40	$275.40
Purchase #2	$45.97	12.262%	$51.6068	$51.61	$51.60	$51.60
Purchase #3	$145.94	7.124%	$156.3368	$156.34	$156.35	$156.30
Purchase #4	$196.38	12.831%	$221.5775	$221.58	$221.60	$221.60
Purchase #5	$34.81	11.656%	$38.8675	$38.87	$38.85	$38.90
Purchase #6	$137.43	9.614%	$150.6425	$150.64	$150.65	$150.60
Purchase #7	$189.64	10.199%	$208.9814	$208.98	$209.00	$209.00
7 purchase totals =	$995.80		$1,103.4079	$1,103.42	$1,103.45	$1,103.40