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	$27.42	10.119%	$30.1946	$30.19	$30.20	$30.20
Purchase #2	$21.44	13.761%	$24.3904	$24.39	$24.40	$24.40
Purchase #3	$67.64	8.368%	$73.3001	$73.30	$73.30	$73.30
Purchase #4	$67.25	5.862%	$71.1922	$71.19	$71.20	$71.20
Purchase #5	$206.71	8.146%	$223.5486	$223.55	$223.55	$223.50
Purchase #6	$234.84	3.734%	$243.6089	$243.61	$243.60	$243.60
Purchase #7	$78.52	5.179%	$82.5866	$82.59	$82.60	$82.60
7 purchase totals =	$703.82		$748.8214	$748.82	$748.85	$748.80