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	$82.72	7.188%	$88.6659	$88.67	$88.65	$88.70
Purchase #2	$82.95	8.654%	$90.1285	$90.13	$90.15	$90.10
Purchase #3	$109.39	13.250%	$123.8842	$123.88	$123.90	$123.90
Purchase #4	$89.91	13.299%	$101.8671	$101.87	$101.85	$101.90
Purchase #5	$248.53	8.627%	$269.9707	$269.97	$269.95	$270.00
Purchase #6	$78.77	11.589%	$87.8987	$87.90	$87.90	$87.90
Purchase #7	$121.77	10.263%	$134.2673	$134.27	$134.25	$134.30
7 purchase totals =	$814.04		$896.6824	$896.69	$896.65	$896.80