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	$77.39	8.251%	$83.7754	$83.78	$83.80	$83.80
Purchase #2	$40.66	3.716%	$42.1709	$42.17	$42.15	$42.20
Purchase #3	$229.49	8.490%	$248.9737	$248.97	$248.95	$249.00
Purchase #4	$181.75	4.289%	$189.5453	$189.55	$189.55	$189.50
Purchase #5	$119.42	11.769%	$133.4745	$133.47	$133.45	$133.50
Purchase #6	$141.46	6.692%	$150.9265	$150.93	$150.95	$150.90
Purchase #7	$170.38	9.437%	$186.4588	$186.46	$186.45	$186.50
7 purchase totals =	$960.55		$1,035.3251	$1,035.33	$1,035.30	$1,035.40