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	$135.79	4.315%	$141.6493	$141.65	$141.65	$141.60
Purchase #2	$93.44	6.201%	$99.2342	$99.23	$99.25	$99.20
Purchase #3	$132.54	8.122%	$143.3049	$143.30	$143.30	$143.30
Purchase #4	$139.83	3.421%	$144.6136	$144.61	$144.60	$144.60
Purchase #5	$149.90	6.187%	$159.1743	$159.17	$159.15	$159.20
Purchase #6	$38.93	4.753%	$40.7803	$40.78	$40.80	$40.80
Purchase #7	$186.88	8.854%	$203.4264	$203.43	$203.45	$203.40
7 purchase totals =	$877.31		$932.1830	$932.17	$932.20	$932.10