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	$147.39	13.221%	$166.8764	$166.88	$166.90	$166.90
Purchase #2	$90.62	9.867%	$99.5615	$99.56	$99.55	$99.60
Purchase #3	$175.62	11.472%	$195.7671	$195.77	$195.75	$195.80
Purchase #4	$229.86	9.574%	$251.8668	$251.87	$251.85	$251.90
Purchase #5	$81.86	9.398%	$89.5532	$89.55	$89.55	$89.60
Purchase #6	$6.60	3.665%	$6.8419	$6.84	$6.85	$6.80
Purchase #7	$225.85	11.346%	$251.4749	$251.47	$251.45	$251.50
7 purchase totals =	$957.80		$1,061.9418	$1,061.94	$1,061.90	$1,062.10