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	$96.35	9.869%	$105.8588	$105.86	$105.85	$105.90
Purchase #2	$210.56	10.742%	$233.1784	$233.18	$233.20	$233.20
Purchase #3	$168.34	10.418%	$185.8777	$185.88	$185.90	$185.90
Purchase #4	$116.38	5.234%	$122.4713	$122.47	$122.45	$122.50
Purchase #5	$135.39	4.607%	$141.6274	$141.63	$141.65	$141.60
Purchase #6	$128.29	10.648%	$141.9503	$141.95	$141.95	$142.00
Purchase #7	$6.27	3.571%	$6.4939	$6.49	$6.50	$6.50
7 purchase totals =	$861.58		$937.4578	$937.46	$937.50	$937.60