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	$27.51	13.142%	$31.1254	$31.13	$31.15	$31.10
Purchase #2	$100.32	5.145%	$105.4815	$105.48	$105.50	$105.50
Purchase #3	$72.46	11.229%	$80.5965	$80.60	$80.60	$80.60
Purchase #4	$131.98	3.400%	$136.4673	$136.47	$136.45	$136.50
Purchase #5	$171.56	5.678%	$181.3012	$181.30	$181.30	$181.30
Purchase #6	$203.55	4.174%	$212.0462	$212.05	$212.05	$212.00
Purchase #7	$246.31	4.641%	$257.7412	$257.74	$257.75	$257.70
7 purchase totals =	$953.69		$1,004.7593	$1,004.77	$1,004.80	$1,004.70