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	$83.32	9.135%	$90.9313	$90.93	$90.95	$90.90
Purchase #2	$165.97	12.419%	$186.5818	$186.58	$186.60	$186.60
Purchase #3	$72.44	13.630%	$82.3136	$82.31	$82.30	$82.30
Purchase #4	$60.35	12.570%	$67.936	$67.94	$67.95	$67.90
Purchase #5	$175.46	3.623%	$181.8169	$181.82	$181.80	$181.80
Purchase #6	$22.50	12.691%	$25.3555	$25.36	$25.35	$25.40
Purchase #7	$137.35	8.375%	$148.8531	$148.85	$148.85	$148.90
7 purchase totals =	$717.39		$783.7882	$783.79	$783.80	$783.80