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	$96.51	10.248%	$106.4003	$106.40	$106.40	$106.40
Purchase #2	$39.47	8.782%	$42.9363	$42.94	$42.95	$42.90
Purchase #3	$23.79	12.387%	$26.7369	$26.74	$26.75	$26.70
Purchase #4	$200.37	10.721%	$221.8517	$221.85	$221.85	$221.90
Purchase #5	$155.55	10.109%	$171.2745	$171.27	$171.25	$171.30
Purchase #6	$71.96	9.383%	$78.712	$78.71	$78.70	$78.70
Purchase #7	$245.27	12.134%	$275.0311	$275.03	$275.05	$275.00
7 purchase totals =	$832.92		$922.9428	$922.94	$922.95	$922.90