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	$54.93	4.740%	$57.5337	$57.53	$57.55	$57.50
Purchase #2	$160.69	7.646%	$172.9764	$172.98	$173.00	$173.00
Purchase #3	$70.67	11.552%	$78.8338	$78.83	$78.85	$78.80
Purchase #4	$82.86	7.765%	$89.2941	$89.29	$89.30	$89.30
Purchase #5	$155.31	11.312%	$172.8787	$172.88	$172.90	$172.90
Purchase #6	$226.77	13.542%	$257.4792	$257.48	$257.50	$257.50
Purchase #7	$166.25	9.109%	$181.3937	$181.39	$181.40	$181.40
7 purchase totals =	$917.48		$1,010.3896	$1,010.38	$1,010.50	$1,010.40