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	$137.81	12.832%	$155.4938	$155.49	$155.50	$155.50
Purchase #2	$80.59	12.241%	$90.455	$90.46	$90.45	$90.50
Purchase #3	$75.79	13.414%	$85.9565	$85.96	$85.95	$86.00
Purchase #4	$170.64	9.785%	$187.3371	$187.34	$187.35	$187.30
Purchase #5	$8.32	10.200%	$9.1686	$9.17	$9.15	$9.20
Purchase #6	$247.27	13.633%	$280.9803	$280.98	$281.00	$281.00
Purchase #7	$229.44	9.742%	$251.792	$251.79	$251.80	$251.80
7 purchase totals =	$949.86		$1,061.1833	$1,061.19	$1,061.20	$1,061.30