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	$80.35	9.802%	$88.2259	$88.23	$88.25	$88.20
Purchase #2	$159.41	8.674%	$173.2372	$173.24	$173.25	$173.20
Purchase #3	$128.61	9.799%	$141.2125	$141.21	$141.20	$141.20
Purchase #4	$216.94	8.325%	$235.0003	$235.00	$235.00	$235.00
Purchase #5	$53.78	9.871%	$59.0886	$59.09	$59.10	$59.10
Purchase #6	$59.59	7.462%	$64.0366	$64.04	$64.05	$64.00
Purchase #7	$24.29	12.843%	$27.4096	$27.41	$27.40	$27.40
7 purchase totals =	$722.97		$788.2107	$788.22	$788.25	$788.10