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	$160.56	8.568%	$174.3168	$174.32	$174.30	$174.30
Purchase #2	$32.90	5.867%	$34.8302	$34.83	$34.85	$34.80
Purchase #3	$25.94	5.302%	$27.3153	$27.32	$27.30	$27.30
Purchase #4	$174.91	6.245%	$185.8331	$185.83	$185.85	$185.80
Purchase #5	$79.36	4.144%	$82.6487	$82.65	$82.65	$82.60
Purchase #6	$249.28	5.856%	$263.8778	$263.88	$263.90	$263.90
Purchase #7	$219.79	7.161%	$235.5292	$235.53	$235.55	$235.50
7 purchase totals =	$942.74		$1,004.3511	$1,004.36	$1,004.40	$1,004.20