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	$37.96	4.652%	$39.7259	$39.73	$39.75	$39.70
Purchase #2	$112.91	9.238%	$123.3406	$123.34	$123.35	$123.30
Purchase #3	$128.62	4.192%	$134.0118	$134.01	$134.00	$134.00
Purchase #4	$197.26	13.416%	$223.7244	$223.72	$223.70	$223.70
Purchase #5	$74.31	11.818%	$83.092	$83.09	$83.10	$83.10
Purchase #6	$90.29	9.752%	$99.0951	$99.10	$99.10	$99.10
Purchase #7	$42.95	5.643%	$45.3737	$45.37	$45.35	$45.40
7 purchase totals =	$684.30		$748.3635	$748.36	$748.35	$748.30