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	$95.38	5.748%	$100.8624	$100.86	$100.85	$100.90
Purchase #2	$137.40	3.557%	$142.2873	$142.29	$142.30	$142.30
Purchase #3	$187.43	6.106%	$198.8745	$198.87	$198.85	$198.90
Purchase #4	$215.51	8.834%	$234.5482	$234.55	$234.55	$234.50
Purchase #5	$148.45	5.150%	$156.0952	$156.10	$156.10	$156.10
Purchase #6	$249.72	8.344%	$270.5566	$270.56	$270.55	$270.60
Purchase #7	$204.46	12.299%	$229.6065	$229.61	$229.60	$229.60
7 purchase totals =	$1,238.35		$1,332.8307	$1,332.84	$1,332.80	$1,332.90