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	$78.25	13.523%	$88.8317	$88.83	$88.85	$88.80
Purchase #2	$191.32	10.199%	$210.8327	$210.83	$210.85	$210.80
Purchase #3	$46.87	5.231%	$49.3218	$49.32	$49.30	$49.30
Purchase #4	$34.70	5.369%	$36.563	$36.56	$36.55	$36.60
Purchase #5	$80.63	13.582%	$91.5812	$91.58	$91.60	$91.60
Purchase #6	$90.77	8.459%	$98.4482	$98.45	$98.45	$98.40
Purchase #7	$75.56	13.437%	$85.713	$85.71	$85.70	$85.70
7 purchase totals =	$598.10		$661.2916	$661.28	$661.30	$661.20