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	$165.51	6.512%	$176.288	$176.29	$176.30	$176.30
Purchase #2	$219.31	6.646%	$233.8853	$233.89	$233.90	$233.90
Purchase #3	$162.57	9.724%	$178.3783	$178.38	$178.40	$178.40
Purchase #4	$133.82	7.302%	$143.5915	$143.59	$143.60	$143.60
Purchase #5	$152.88	7.867%	$164.9071	$164.91	$164.90	$164.90
Purchase #6	$30.49	6.539%	$32.4837	$32.48	$32.50	$32.50
Purchase #7	$59.54	5.464%	$62.7933	$62.79	$62.80	$62.80
7 purchase totals =	$924.12		$992.3272	$992.33	$992.40	$992.40