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	$180.37	11.148%	$200.4776	$200.48	$200.50	$200.50
Purchase #2	$93.81	3.279%	$96.886	$96.89	$96.90	$96.90
Purchase #3	$11.75	12.280%	$13.1929	$13.19	$13.20	$13.20
Purchase #4	$111.46	3.852%	$115.7534	$115.75	$115.75	$115.80
Purchase #5	$233.47	9.591%	$255.8621	$255.86	$255.85	$255.90
Purchase #6	$85.32	4.106%	$88.8232	$88.82	$88.80	$88.80
Purchase #7	$135.90	10.624%	$150.338	$150.34	$150.35	$150.30
7 purchase totals =	$852.08		$921.3332	$921.33	$921.35	$921.40