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	$37.84	12.867%	$42.7089	$42.71	$42.70	$42.70
Purchase #2	$148.80	13.419%	$168.7675	$168.77	$168.75	$168.80
Purchase #3	$135.89	3.250%	$140.3064	$140.31	$140.30	$140.30
Purchase #4	$162.89	13.213%	$184.4127	$184.41	$184.40	$184.40
Purchase #5	$203.83	11.769%	$227.8188	$227.82	$227.80	$227.80
Purchase #6	$7.45	9.775%	$8.1782	$8.18	$8.20	$8.20
Purchase #7	$225.25	3.744%	$233.6834	$233.68	$233.70	$233.70
7 purchase totals =	$921.95		$1,005.8759	$1,005.88	$1,005.85	$1,005.90