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	$115.61	4.629%	$120.9616	$120.96	$120.95	$121.00
Purchase #2	$245.91	4.267%	$256.403	$256.40	$256.40	$256.40
Purchase #3	$148.47	13.656%	$168.7451	$168.75	$168.75	$168.70
Purchase #4	$134.98	7.398%	$144.9658	$144.97	$144.95	$145.00
Purchase #5	$73.77	6.285%	$78.4064	$78.41	$78.40	$78.40
Purchase #6	$59.40	12.815%	$67.0121	$67.01	$67.00	$67.00
Purchase #7	$71.46	10.689%	$79.0984	$79.10	$79.10	$79.10
7 purchase totals =	$849.60		$915.5924	$915.60	$915.55	$915.60