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	$88.85	3.137%	$91.6372	$91.64	$91.65	$91.60
Purchase #2	$18.82	8.780%	$20.4724	$20.47	$20.45	$20.50
Purchase #3	$157.89	6.686%	$168.4465	$168.45	$168.45	$168.40
Purchase #4	$154.44	12.692%	$174.0415	$174.04	$174.05	$174.00
Purchase #5	$47.59	4.647%	$49.8015	$49.80	$49.80	$49.80
Purchase #6	$82.58	3.299%	$85.3043	$85.30	$85.30	$85.30
Purchase #7	$29.73	4.497%	$31.067	$31.07	$31.05	$31.10
7 purchase totals =	$579.90		$620.7704	$620.77	$620.75	$620.70