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	$28.27	11.134%	$31.4176	$31.42	$31.40	$31.40
Purchase #2	$6.56	4.154%	$6.8325	$6.83	$6.85	$6.80
Purchase #3	$164.45	4.758%	$172.2745	$172.27	$172.25	$172.30
Purchase #4	$156.99	9.184%	$171.408	$171.41	$171.40	$171.40
Purchase #5	$240.82	12.476%	$270.8647	$270.86	$270.85	$270.90
Purchase #6	$19.97	13.582%	$22.6823	$22.68	$22.70	$22.70
Purchase #7	$109.47	6.313%	$116.3808	$116.38	$116.40	$116.40
7 purchase totals =	$726.53		$791.8604	$791.85	$791.85	$791.90