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	$70.60	8.304%	$76.4626	$76.46	$76.45	$76.50
Purchase #2	$23.75	6.708%	$25.3432	$25.34	$25.35	$25.30
Purchase #3	$154.88	12.705%	$174.5575	$174.56	$174.55	$174.60
Purchase #4	$189.53	5.729%	$200.3882	$200.39	$200.40	$200.40
Purchase #5	$155.33	10.268%	$171.2793	$171.28	$171.30	$171.30
Purchase #6	$58.55	7.392%	$62.878	$62.88	$62.90	$62.90
Purchase #7	$101.30	7.600%	$108.9988	$109.00	$109.00	$109.00
7 purchase totals =	$753.94		$819.9076	$819.91	$819.95	$820.00