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	$247.31	4.258%	$257.8405	$257.84	$257.85	$257.80
Purchase #2	$78.91	5.668%	$83.3826	$83.38	$83.40	$83.40
Purchase #3	$218.50	6.815%	$233.3908	$233.39	$233.40	$233.40
Purchase #4	$212.39	10.651%	$235.0117	$235.01	$235.00	$235.00
Purchase #5	$71.80	9.168%	$78.3826	$78.38	$78.40	$78.40
Purchase #6	$140.73	4.714%	$147.364	$147.36	$147.35	$147.40
Purchase #7	$113.33	5.384%	$119.4317	$119.43	$119.45	$119.40
7 purchase totals =	$1,082.97		$1,154.8039	$1,154.79	$1,154.85	$1,154.80