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	$232.51	3.303%	$240.1898	$240.19	$240.20	$240.20
Purchase #2	$187.81	10.168%	$206.9065	$206.91	$206.90	$206.90
Purchase #3	$199.61	6.148%	$211.882	$211.88	$211.90	$211.90
Purchase #4	$67.96	4.724%	$71.1704	$71.17	$71.15	$71.20
Purchase #5	$101.62	3.664%	$105.3434	$105.34	$105.35	$105.30
Purchase #6	$140.85	9.227%	$153.8462	$153.85	$153.85	$153.80
Purchase #7	$133.96	12.554%	$150.7773	$150.78	$150.80	$150.80
7 purchase totals =	$1,064.32		$1,140.1156	$1,140.12	$1,140.15	$1,140.10