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	$37.29	13.806%	$42.4383	$42.44	$42.45	$42.40
Purchase #2	$219.38	4.670%	$229.625	$229.63	$229.65	$229.60
Purchase #3	$153.40	13.795%	$174.5615	$174.56	$174.55	$174.60
Purchase #4	$76.51	6.415%	$81.4181	$81.42	$81.40	$81.40
Purchase #5	$24.67	9.540%	$27.0235	$27.02	$27.00	$27.00
Purchase #6	$181.37	8.274%	$196.3766	$196.38	$196.40	$196.40
Purchase #7	$195.55	5.657%	$206.6123	$206.61	$206.60	$206.60
7 purchase totals =	$888.17		$958.0553	$958.06	$958.05	$958.00