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	$238.27	8.410%	$258.3085	$258.31	$258.30	$258.30
Purchase #2	$114.82	8.617%	$124.714	$124.71	$124.70	$124.70
Purchase #3	$79.77	6.736%	$85.1433	$85.14	$85.15	$85.10
Purchase #4	$223.67	10.551%	$247.2694	$247.27	$247.25	$247.30
Purchase #5	$225.59	7.871%	$243.3462	$243.35	$243.35	$243.30
Purchase #6	$108.59	3.780%	$112.6947	$112.69	$112.70	$112.70
Purchase #7	$103.67	8.173%	$112.1429	$112.14	$112.15	$112.10
7 purchase totals =	$1,094.38		$1,183.6190	$1,183.61	$1,183.60	$1,183.50